Pathogenic Mechanisms and Host Interactions in Staphylococcus epidermidis Device-Related Infection
- 1Musculoskeletal Infection, AO Research Institute Davos, Davos, Switzerland
- 2Molecular Immunology, Swiss Institute of Allergy and Asthma Research, University of Zurich, Davos, Switzerland
- 3Microbiology and Infectious Diseases, Institute of Life Science, Swansea University Medical School, Swansea, United Kingdom
- 4Department of Orthopedic and Trauma Surgery, University Hospital Basel, Basel, Switzerland
Staphylococcus epidermidis is a permanent member of the normal human microbiota, commonly found on skin and mucous membranes. By adhering to tissue surface moieties of the host via specific adhesins, S. epidermidis is capable of establishing a lifelong commensal relationship with humans that begins early in life. In its role as a commensal organism, S. epidermidis is thought to provide benefits to human host, including out-competing more virulent pathogens. However, largely due to its capacity to form biofilm on implanted foreign bodies, S. epidermidis has emerged as an important opportunistic pathogen in patients receiving medical devices. S. epidermidis causes approximately 20% of all orthopedic device-related infections (ODRIs), increasing up to 50% in late-developing infections. Despite this prevalence, it remains underrepresented in the scientific literature, in particular lagging behind the study of the S. aureus. This review aims to provide an overview of the interactions of S. epidermidis with the human host, both as a commensal and as a pathogen. The mechanisms retained by S. epidermidis that enable colonization of human skin as well as invasive infection, will be described, with a particular focus upon biofilm formation. The host immune responses to these infections are also described, including how S. epidermidis seems to trigger low levels of pro-inflammatory cytokines and high levels of interleukin-10, which may contribute to the sub-acute and persistent nature often associated with these infections. The adaptive immune response to S. epidermidis remains poorly described, and represents an area which may provide significant new discoveries in the coming years.
Staphylococcus epidermidis is a permanent member of the normal human microbiota, commonly found on skin, and mucous membranes. By adhering to tissue surface moieties of the host via specific adhesins, S. epidermidis is capable of establishing a lifelong commensal relationship with humans that begins early in life. Although commensal S. epidermidis isolates display high rates of resistance to antibiotics of clinical relevance (Morgenstern et al., 2016a), their default status as commensal bacteria renders this phenomenon largely irrelevant for the healthy human host. However, with the advent of implanted medical devices such as prosthetic joints and fracture fixation devices, S. epidermidis has emerged as an important opportunistic pathogen (Otto, 2009; Widerstrom, 2016). In fact, the implanted medical device may actually facilitate infection since any S. epidermidis inadvertently introduced into the surgical site are capable of rapidly adhering to, and accumulating upon, the surface of the device. This surface-associated bacterial growth is known as biofilm formation and appears to be the key factor enabling invasive, device-related infection (DRI) for an otherwise largely non-pathogenic microorganism. The ubiquitous presence of S. epidermidis on human skin has enabled S. epidermidis infection to emerge as a significant complication when using medical devices (Rogers et al., 2009; Montanaro et al., 2011; Hogan et al., 2015). With the increasing use of such devices, coupled with high antibiotic resistance rates, S. epidermidis DRI will likely remain a clinical problem for generations to come.
This review describes host interactions with S. epidermidis under both healthy commensal conditions, and under conditions of an invasive DRI. This includes describing how this microorganism has adapted to life on human skin, including biofilm formation, and how the same adaptations have enabled invasive DRI. Particular attention will be paid to the impact of S. epidermidis in orthopedic device-related infection (ODRI) since these infections are amongst the most burdensome and expensive to treat (Darouiche, 2004). Finally, since the impact of ODRI on bone tissue is a critical feature of these infections, interactions between S. epidermidis and bone will also be described.
S. epidermidis as a Member of Commensal Human Microbiota
Under healthy conditions, the skin commensal microbiota is believed to be beneficial to humans through aiding in nutrition, outcompeting pathogens and educating the immune system (Brown and Clarke, 2017). Humans are believed to first encounter S. epidermidis in utero, as evidenced by their presence in amniotic fluid (Collado et al., 2016). The first feces (meconium) has also been shown to harbor a predominance of S. epidermidis (Jimenez et al., 2008) and the skin of the newborn will be colonized by S. epidermidis within a few days (Dominguez-Bello et al., 2010). Thereafter, S. epidermidis becomes part of the “normal” resident human skin microbiota, being predominant in moist sites such as nares or fossae, but also present in sebaceous areas such as the facial skin (Grice et al., 2009) and mucosal tissues such as the gastrointestinal and the lower reproductive tracts (Sharon et al., 2013; Majchrzak et al., 2016).
In order to persist on human skin, S. epidermidis has evolved diverse mechanisms to sense and overcome the physical and chemical features of host antimicrobial defense. Such mechanisms include surface adhesins enabling attachment to the host (Coates et al., 2014), systems to sense host antimicrobial peptides (AMPs) and communication molecules (e.g., hormones) (Li et al., 2007; N'Diaye et al., 2016), mechanisms against AMPs (Joo and Otto, 2015) (e.g., S. epidermidis derived protease SepA is induced by and directed against the human AMP dermicidin; Lai et al., 2007), and survival strategies against desiccation and osmotic stress (Hirai, 1991; Amin et al., 1995).
S. epidermidis has also been shown to influence host colonization by other species, as shown for Staphylococcus aureus (Iwase et al., 2010; Park et al., 2011). Negative correlations between these two species have been reported in humans, insinuating an antagonism between at least some strains (Frank et al., 2010; Sullivan et al., 2016). This effect is at least partially due to the secretion of factors that impact on the viability or colonization capacity of other microorganisms (Christensen et al., 2016; Janek et al., 2016). Phenol soluble modulins (PSMs) are a family of multifunctional amphipathic, alpha-helical peptides that are produced by S. epidermidis isolates (Otto, 2014). They are believed to act upon host cells, are important for biofilm maturation (Wang et al., 2011) and could play a role in the competition between microorganisms on human skin. In particular, PSM-γ and PSM-δ produced by S. epidermidis have been shown to selectively reduce survival of Streptococcus pyogenes on mouse skin, but did not affect S. epidermidis itself (Cogen et al., 2010a,b). Both PSM-γ and PSM-δ cause membrane leakage in target bacteria (S. aureus and S. pyogens) (Cogen et al., 2010b), which indicates that they function like host-derived AMPs, with whom they share structural similarities. Host-derived AMPs and S. epidermidis PSMs have even been shown to act synergistically against bacterial pathogens (Cogen et al., 2010a). In contrast, the closely related δ-toxin of S. aureus only seems to possess a very limited antimicrobial activity (Dhople and Nagaraj, 1993, 2005) suggesting that the cooperative effect with host AMPs is not a widespread phenomenon. In addition, many strains of S. epidermidis also produce bacteriocins, which are antimicrobial peptides that act against other species or strains (often closely related to the producing bacteria). Gram-positive bacteria usually produce two types of bacteriocins: lanthionine-containing antibacterial peptides (lantibiotics) and class-II bacteriocins (Bastos et al., 2009; Hassan et al., 2012). For S. epidermidis, examples include the lantibiotics epidermin (Allgaier et al., 1986), Pep5, epilancin K7 (van de Kamp et al., 1995), and epilancin 15X (Ekkelenkamp et al., 2005), with further examples recently described (Sandiford and Upton, 2012; Bennallack et al., 2014; Janek et al., 2016). Another mechanism employed by S. epidermidis to compete with other skin microorganisms involves the degradation of biofilms from other bacterial species. The serine protease Esp is able to mediate S. aureus biofilm degradation by targeting several proteins involved in biofilm assembly (Iwase et al., 2010; Sugimoto et al., 2013). It has been observed that the presence of Esp-secreting S. epidermidis in the nose correlates with the absence of S. aureus in healthy human volunteers (Iwase et al., 2010). This activity has been supported experimentally with the finding that the intranasal application of an Esp-secreting strain was able to decrease S. aureus colonization in mice and humans (Iwase et al., 2010; Park et al., 2011). Finally, metabolic products may also serve to counteract other microorganisms. S. epidermidis has been shown to ferment glycerol into short chain fatty acids, which have displayed inhibitory activity against Propionibacterium acnes (implicated in acne vulgaris) in vitro and in mice (Wang et al., 2014).
S. epidermidis as a Pathogen
In contrast to its standard role as a commensal microorganism, S. epidermidis and other coagulase negative Staphylococci (CoNS) have been found to cause invasive infections in selected groups of patients. These higher risk groups include preterm neonates, immunocompromised individuals and patients with indwelling medical devices (Darouiche, 2004; Bjorkqvist et al., 2010; Dong and Speer, 2014). Unlike S. aureus, which typically produces numerous extracellular enzymes and toxins that enable invasive infections in otherwise healthy hosts, S. epidermidis seems to retain a limited number of virulence factors (Gill et al., 2005) and normally is unable to cause invasive infection in healthy hosts (Heilmann and Gotz, 2013).
S. epidermidis as a Pathogen of the Musculoskeletal System
S. epidermidis is second only to S. aureus as the most prevalent species encountered in ODRIs (Trampuz and Zimmerli, 2005, 2006). S. epidermidis causes approximately 20–30% of ODRIs (Trampuz and Zimmerli, 2006; Montanaro et al., 2011; Moriarty et al., 2016) and the prevalence may even increase to 50% in late-developing infections (Schafer et al., 2008). These late-developing infections may be linked to the sub-acute nature of S. epidermidis infections, which may present many months after surgery with subtle signs of infection. This differs from the acute and often obvious nature of S. aureus infections and may be partially explained by the lack of virulence factors retained by S. epidermidis in comparison with S. aureus (Melzer et al., 2003; Zimmerli et al., 2004; Shurland et al., 2007).
The diagnosis of ODRI is based on the combination of clinical presentation, biopsy culture, histological analysis and clinical diagnostic criteria, such as high C-reactive protein (Metsemakers et al., 2016). Diagnosis may be particularly challenging for sub-acute infections due to the lack of obvious clinical signs of infection. Therefore, microbiological culture results are often the most critical diagnostic criteria. Since the microbes grow in biofilms on the foreign material and in necrotic bone tissue, cultivation and identification of the disease-causing pathogens may require the culture of several intraoperative tissue samples and removal of the implant for appropriate sampling (Costerton et al., 2011; Xu et al., 2017). To increase the yield of positive cultures, it is advised to terminate antibiotic therapy before sampling, acquire at least three tissue biopsies, and to perform sonication of removed hardware to remove biofilm-associated bacteria from the surface (Trampuz and Zimmerli, 2006; Trampuz et al., 2007; Puig-Verdie et al., 2013; Yano et al., 2014; Dapunt et al., 2015; Metsemakers et al., 2016). In suspected S. epidermidis infections, where the pathogen is also a skin commensal that could contaminate the biopsy if aseptic techniques are not followed, the same indistinguishable microorganism must be cultured from at least two separate biopsies in order to differentiate a relevant infection from skin contamination. In contrast, in virulent species such as S. aureus or Escherichia coli, a single positive biopsy may be sufficient to determine the presence of an infection (Patzakis and Zalavras, 2005; Osmon et al., 2013).
The treatment of S. epidermidis ODRI will depend on patient-specific factors, but will possibly require implant removal and a minimum of 6 weeks antibiotic therapy (Trampuz and Zimmerli, 2005, 2006; Moriarty et al., 2016). Despite such prolonged and comprehensive therapy, infection recurs in approximately one third of the cases and up to one fifth of cases cannot achieve a cure with restoration of limb function (Salgado et al., 2007; Teterycz et al., 2010; Morgenstern et al., 2016b,c). Morgenstern et al. investigated the clinical course and outcome of staphylococcal ODRIs in elderly patients and could show that S. epidermidis was associated with prolonged infections and was associated with lower cure rates (75%) than S. aureus (84%), although S. aureus related infections were associated with a five-fold higher mortality rate (Morgenstern et al., 2016b). This data therefore supports clinical beliefs that S. epidermidis is an agent of sub-acute infection with significantly worse treatment outcomes, although those infections may be less life-threatening than S. aureus infections.
S. epidermidis Virulence Factors
Adhesion to Host Proteins
As a commensal microorganism, S. epidermidis retains the ability to specifically adhere to host proteins in the skin. In a surgical wound, the bacterium utilizes these adhesion mechanisms in order to adhere to the deeper tissues and to the implanted device, or more specifically, the conditioning layer of host proteins deposited upon the device. Initial adhesion of bacteria to implant surfaces is mediated by non-specific interactions such as hydrophobic interactions (Gristina, 1987), and then as shown schematically in Figure 1, by specific adhesins such as autolysin (AtlE) (Heilmann et al., 1997), extracellular DNA (eDNA) (Qin et al., 2007; Izano et al., 2008), and staphylococcal surface protein 1 and 2 (SSP-1, SSP-2) (Veenstra et al., 1996). AtlE, SSP-1, and SSP-2 have been primarily associated with adhesion to native surfaces (Veenstra et al., 1996; Heilmann et al., 1997), whilst eDNA is generated in S. epidermidis through an AtlE-mediated lysis of a subpopulation of the bacteria, promoting biofilm formation within the remaining population (Qin et al., 2007). In the context of medical devices, the surface of the device becomes coated with host-derived plasma proteins, extracellular matrix (ECM) proteins and coagulation products (platelets and thrombin) immediately following implantation (Baier et al., 1984). Cell-wall-anchored (CWA) proteins/adhesins, such as the microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) (Foster and Hook, 1998) bind bacteria like S. epidermidis directly to these molecules (Figure 2). In S. epidermidis, adhesins for fibrinogen [as serine-aspartate repeat protein G (SdrG/Fbe) (Hartford et al., 2001; Brennan et al., 2009)], fibronectin [extracellular matrix-binding protein (Embp) (Arciola et al., 2003)], collagen [SdrF/GehD (Bowden et al., 2002; Arrecubieta et al., 2007)], vitronectin [AtlE or autolysin/adhesin (Aae) (Heilmann et al., 2003)] and elastin [elastin-binding protein (EbpS)] have all been identified. Peptidoglycan-bound wall teichoic acids (WTA) are an essential part of the S. epidermidis cell wall and also play an important role in bacterial adhesion. WTA enhances the initial adhesion of S. epidermidis to medical devices by binding to adsorbed fibronectin (Hussain et al., 2001) and fibrin clots (Chugh et al., 1990).
Figure 1. Biofilm formation scheme with scanning electron micrographs of S. epidermidis single cells (lower left) or in biofilm community surrounded by EPS (lower right) on a titanium surface. Image adapted with permission from Moriarty et al. (2011).
Figure 2. Scheme of the main S. epidermidis pathogenic mechanisms, which include adhesion molecules and biofilm formation. The most well described adhesins involved in adhesion to native surfaces or protein-coated surfaces are shown in the upper part (molecules also involved in biofilm formation shown in purple). The main described biofilm components are shown at the bottom of the figure (PIA, cleaved Aap, eDNA, WTA, and Empb). The figure also presents some of the most important regulators of biofilm and adhesion molecules (black arrows: activation/positive signaling, red lines: inhibition/negative signaling). See text for further details.
The ability to adhere to a surface represents the first step in biofilm formation, commonly believed to be the most important virulence factor possessed by S. epidermidis (Figure 1). Biofilm development facilitates resistance against host defense mechanisms (Myrvik et al., 1989; Kristian et al., 2008; Cerca et al., 2011; Schommer et al., 2011) and confers antibiotic resistance (Cerca et al., 2006; Mack et al., 2006). Biofilm formation also complicates medical and surgical treatment protocols because implant removal is often required to remove the biofilm.
Biofilms are defined as complex communities of adherent bacteria encased in a matrix of self-produced extracellular polymeric substances (EPS) (Costerton et al., 1995) (Figure 1). The accumulation and maturation of the S. epidermidis biofilm occurs via a number of mechanisms. Polysaccharide intercellular adhesin [PIA, or poly-N-acetyl-glucosamine (PNAG)], synthesized by icaADBC encoded proteins (Heilmann et al., 1996; Mack et al., 1996a) is responsible for biofilm formation in the majority of S. epidermidis isolates (Mack et al., 1996b) and was believed to be the most common molecule associated with biofilm formation (Heilmann et al., 1996; Mack et al., 1996a; Figure 2). This was endorsed by the observation that the ica operon was absent in most commensal S. epidermidis strains (Zhang et al., 2003; Chokr et al., 2007). However, not all S. epidermidis have the icaADBC genes (Heilmann et al., 1996; Harris et al., 2016) and these isolates mediate biofilm formation by proteinaceous factors, such as the accumulation associated protein (Aap) (Rohde et al., 2005) that contributes to biofilm formation upon cleavage by extracellular or host proteases (Figure 2). The aap gene has been observed in both pathogenic and commensal isolates, more frequently than the ica operon (Gill et al., 2005; Los et al., 2010; Harris et al., 2016). Other PIA-independent mechanisms include biofilm associated homolog protein (Bhp) (Bowden et al., 2005; Tormo et al., 2005), Embp (Williams et al., 2002; Christner et al., 2010), and S. epidermidis surface protein (Ses)C (Shahrooei et al., 2009), and SesE (Harris et al., 2016). Interestingly, Rohde et al. suggested that PIA-dependent biofilms are more robust than those formed by proteinaceous factors (Rohde et al., 2007), and another study found they result in a different morphotype or biofilm substructure (Harris et al., 2016). WTA have also been linked with S. epidermidis biofilm formation. TagO encodes the first enzymatic step in WTA biosynthesis and a tagO mutant has been shown to have a biofilm negative phenotype. This is partly attributed to an increase in cell surface hydrophobicity, impairing its initial adhesion to the surface, and a decreased production of PIA by activating the icaADBC repressor, icaR (Holland et al., 2011).
Both CWA proteins and biofilm formation mechanisms are regulated by several global regulators, such as the accessory gene regulator (agr), staphylococcal accessory homologous sar genes, sigma factor B (σB), and luxS (Vuong et al., 2003; Knobloch et al., 2004; Xu et al., 2006; Christner et al., 2012). Further information on regulation of biofilm in S. epidermidis can be obtained in other review articles (Kong et al., 2006; Mack et al., 2007; Le and Otto, 2015; Paharik and Horswill, 2016).
As already mentioned, biofilms play a role in immune evasion, primarily by providing a barrier to immune cells. PIA may contribute to innate immune system evasion by promoting generation of complement C5a fragment (Satorius et al., 2013; Al-Ishaq et al., 2015), inhibiting phagocytes and neutrophil killing (Vuong et al., 2004b,c), and reducing the activity of AMPs (Vuong et al., 2004b; Otto, 2006). Recently, other studies have reported slightly opposite findings, with PIA-producing bacteria inducing greater inflammatory responses and enhanced phagocytosis (Spiliopoulou et al., 2012; Ferreirinha et al., 2016), although Spiliopoulou et al. did observe reduced killing in PIA-producing strains as discussed elsewhere recently (Nguyen et al., 2017). S. epidermidis also produces a second exopolymer, the poly-γ-glutamic acid (PGA), although at comparatively lower levels. Synthesized by the gene products of the cap locus, PGA is important in mediating S. epidermidis resistance to neutrophil phagocytosis and AMPs, and promoting growth at high salt concentrations (PGA is induced under such conditions) (Kocianova et al., 2005).
It has yet to be elucidated if WTA has a direct role in S. epidermidis immune system evasion. However, like S. aureus, S. epidermidis contains the genes for D-alanylation of WTA, a modification known to protect the bacteria from the activity of AMPs (Peschel et al., 1999).
Although the majority of S. epidermidis strains remain susceptible to the newer antibiotics such as daptomycin, tigecycline, linezolid and dalbavancin (Hellmark et al., 2009; Pinheiro et al., 2016), high endemic antimicrobial resistance within this species represents a significant challenge in the treatment of S. epidermidis infections, especially DRI (Diekema et al., 2001). Methicillin resistance in S. epidermidis (MRSE) is an important characteristic of infecting isolates as it is often associated with additional antibiotic resistance mechanisms. Resistance to other antibiotics, such as erythromycin (encoded by erm genes), ciprofloxacin, clindamycin, aminoglycosides (encoded in aacA/aphD gene) or trimethoprim-sulfamethoxazole, are also often observed, especially in MRSE (Cherifi et al., 2013). Methicillin resistance is encoded by mecA, an alternative penicillin binding protein with decreased affinity to β-lactam based antibiotics such as penicillin, methicillin and oxacillin (Chambers et al., 1985). It is carried on the mobile genetic element, staphylococcal cassette chromosome mec (SCCmec), of which several types have been identified for S. epidermidis (Miragaia et al., 2005). MRSE have been found to be common in infection-causing isolates (70–87% of all S. epidermidis isolates) (Cherifi et al., 2013; Farina et al., 2016; Morgenstern et al., 2016c; Salgueiro et al., 2017), and even higher (90%) in specific patient cohorts (Morgenstern et al., 2016b). MRSE prevalence in healthy individuals is low (3–18% of S. epidermidis commensal isolates) (Rolo et al., 2012; Cherifi et al., 2013; Farina et al., 2016), although prevalence is increased for individuals exposed to the healthcare system, as observed in hospitalized patients or in healthcare workers (Rohde et al., 2004; Morgenstern et al., 2016a; Widerstrom et al., 2016). The specific causes of the increased prevalence of resistant isolates in the hospital environment is unknown, although is likely associated with high antibiotic exposure and direct or indirect interpersonal transmission.
It remains unclear whether infection with resistant organisms results in a worse clinical outcome in comparison with susceptible counterparts. In a recent study of patients with S. epidermidis ODRIs, methicillin resistance status did not influence the clinical course and outcome of treatment (Morgenstern et al., 2016c), although further studies are required to confirm this finding. In any case, clear therapeutic guidelines are available for the treatment of both MRSE and MSSE, with a high likelihood of treatment success in both cases when guidelines are followed closely.
Phenol Soluble Modulins
Until relatively recently it was thought that S. epidermidis did not produce toxins. However, the identification and characterization of the PSMs have now changed that concept (Mehlin et al., 1999). The PSMs are a family of genome-encoded peptides, and like the CWA proteins/adhesins, are under the strict regulation of the agr quorum sensing system (Figure 2; Mehlin et al., 1999; Vuong et al., 2004a; Yao et al., 2005). In S. epidermidis, the PSM family consists of PSM-α, PSM-β1, PSM-β2, PSM-δ, PSM-ε, and PSM-γ/δ-toxin (Mehlin et al., 1999; Vuong et al., 2004a; Yao et al., 2005). PSMβ peptides are the primary PSMs produced by S. epidermidis, are expressed at high levels during biofilm formation, and have been shown to have a role in the structuring and dispersal of the biofilm (Yao et al., 2005; Wang et al., 2011). They are specifically associated with the formation of channels observed between the biofilm layers, which are considered important for nutrient uptake (Wang et al., 2011). S. epidermidis-derived PSMδ is strongly cytolytic against neutrophils, similar to S. aureus. However, S. epidermidis culture filtrates were observed to have a very low cytolytic potential in vitro (Cheung et al., 2010). As growing conditions are likely to have an influence on PSM production, the role of S. epidermidis PSMδ in vivo needs to be further addressed.
Finally, certain S. epidermidis strains have been shown to produce PSM-mec, a PSM encoded in the mobile genetic element SCCmec, in contrast to the other PSMs that are chromosomal encoded (Qin et al., 2016). PSM-mec has cytolytic potential against neutrophils in vitro and its presence has been associated with decreased bacterial clearance and higher mortality rates in a murine model of sepsis (Qin et al., 2017).
Other Pathogenic Mechanisms
Small colony variants (SCVs), a colony phenotype characterized by small size, slow growth and downregulation of virulence genes, are recognized as a pathogenic mechanism for several bacterial species, including S. epidermidis, and are often associated with chronic infections (Johns et al., 2015). SCVs seem to be less susceptible to antibiotics and to the immune system, potentially by being able to survive intracellularly and inducing a more anti-inflammatory environment due to increased secretion of IL-10 (Magrys et al., 2015). The topic has been extensively reviewed recently (Kahl et al., 2016).
Finally, internalization and intracellular persistence in non-professional phagocytes (e.g., osteoblasts) is a described evasion mechanism for S. aureus (Mempel et al., 2002; Hamza and Li, 2014). A few internalization mechanisms have been described for S. epidermidis, involving AtlE (Hirschhausen et al., 2010) and SdrG (Claro et al., 2015). This represents a potentially new pathogenic mechanism for S. epidermidis and a location where bacteria could survive to cause persistent/relapsing infections; however its relevance in vivo has not yet been proven.
Host Interaction with S. epidermidis
The interaction between S. epidermidis as a commensal with the host immune system is thought to play a role in the development of immunological tolerance. That is, to induce immune responses in the host which control aberrant inflammatory responses to non-pathogenic molecules such as those found in food but also in commensal bacteria. This question was assessed in recent murine studies with the topical application of S. epidermidis (Naik et al., 2015; Scharschmidt et al., 2015) (S. epidermidis is typically not a major representative of the normal mouse skin microbiota; Tavakkol et al., 2010). Scharschmidt et al. reported that the application of S. epidermidis to the skin within the first weeks of life established antigen-specific tolerance to the bacteria, by generating CD4+ regulatory T (Treg) cells, which homed into neonatal skin (Scharschmidt et al., 2015). Mice that were not colonized during the neonatal period presented with higher inflammation and neutrophil recruitment compared to colonized mice, when challenged with the same strain of S. epidermidis in a skin-abrasion model. The use of the sphingosine-1-phosphate receptor antagonist FTY720 during neonatal period, which blocked the egression of Tregs into skin, suppressed the tolerogenic effect indicating that there may exist a critical period when Treg mediated tolerance can be acquired (Scharschmidt et al., 2015). On the other hand, Naik et al. showed that S. epidermidis application induced cutaneous interferon (IFN)-γ and interleukin (IL)-17A producing T cells (Naik et al., 2015). In this case, IL-17A+CD8+ T cells were shown to home to the mouse epidermis specifically after S. epidermidis application, but not with other tested species. This was mediated through the action of a skin-resident dendritic cell subset and was not associated with the induction of inflammation (Naik et al., 2015). More importantly, when an epicutaneous infection model with Candida albicans was used, the application of the fungus in mice pretreated with topical S. epidermidis resulted in decreased C. albicans CFU counts compared to not pretreated ones. The effect was lost when either anti-CD8 or anti-IL-17A antibodies were co-administered, which highlights the relevance of the adaptive immune responses generated. Altogether, the study suggested that resident bacteria in the skin (S. epidermidis) can modulate the immune system, generating adaptive immune responses which in turn may help in promoting protective innate immune responses and controlling inflammation. The effect seemed to be tissue-specific, since S. epidermidis failed to induce IL-17A-producing cells when administered in the lung or gut. In two other studies, S. epidermidis lipoteichoic acid (LTA) has been shown to decrease skin inflammation (Lai et al., 2009), for example by inducing regulatory microRNAs in a Pseudomonas aeruginosa skin infection model (Xia et al., 2016). However, the true nature of these observations needs to be clarified, as LTA purity even from commercial preparations has been questioned (Nguyen et al., 2017).
Overall, these experimental data reveal the capacity of “commensal” S. epidermidis to specifically shape cutaneous immunity (innate and adaptive responses) and consequently decrease infection burden in the host. The capacity of S. epidermidis to induce similar effects in humans remains to be proven. Nevertheless, this idea can be somewhat supported by in vitro findings, whereby human monocytes, monocyte-derived dendritic cells (moDC) and T lymphocytes stimulated with S. epidermidis displayed an anti-inflammatory profile, with high production of IL-10 (Laborel-Preneron et al., 2015). Further in vivo and human microbiome studies may provide a deeper understanding of the complex nature of this microorganism-host interaction.
Innate Immune Response during Infection
Innate immune responses are triggered by the detection of microbial structures through pattern-recognition receptors (PRRs) on immune and tissue cells. The most studied PRRs are toll-like receptors (TLRs), which recognize a broad range of bacterial derived macromolecules (Akira and Hemmi, 2003). S. epidermidis triggers immune responses partly via TLR-2 (which often forms heterodimers with TLR-1 and TLR-6; Fournier, 2012), similar to S. aureus (Yoshimura et al., 1999; Morath et al., 2002). TLR-2 can recognize different bacterial cell wall molecules including lipoproteins, LTA and peptidoglycan (PDG) (Figure 3; Akira et al., 2006; Fournier, 2012), although some of its ligands are still controversial (van Bergenhenegouwen et al., 2013). Secreted components can also be recognized and activate the immune system, as it was shown for S. epidermidis PSM, which is recognized by TLR-2/TLR-6 heterodimers (Hajjar et al., 2001).
Figure 3. Summary of S. epidermidis recognition and subsequent effector mechanisms. Recognition of S. epidermidis or its secreted proteins can occur via TLR-2 (in red), which forms heterodimers with TLR-1 and TLR-6 and can also associate with other non-TLR molecules (unspecified partner colored in blue). Other receptors recognizing S. epidermidis include CD14 and FPR2/ALX. Upon recognition, downstream signaling and effector mechanisms are triggered, including secretion of AMPs, phagocytosis by neutrophils and macrophages and secretion of cytokines and chemokines from numerous cell types, which will orchestrate additional innate and adaptive immune responses.
Recognition of S. epidermidis via TLR-2 has been shown in keratinocytes (Wanke et al., 2011; Ommori et al., 2013), endothelial cells (Robertson et al., 2010), or human fibroblasts (Hatakeyama et al., 2003), and has also been demonstrated in TLR-2 transfected human embryonic kidney (HEK)293 cell line (Strunk et al., 2010). Furthermore, in preclinical models of S. epidermidis bacteremia or subcutaneous/soft tissue foreign-body infection, an up-regulation of TLR-2 and the adaptor molecule MyD88 has been observed upon infection (Kronforst et al., 2012; Svensson et al., 2015, 2017). The use of TLR-2 knock-out (KO) in bacteremia models with neonatal and adult mice resulted in delayed clearance, especially at early time-points after infection (Strunk et al., 2010; Bi et al., 2015; Cole et al., 2016). These data suggest that TLR-2 is involved in the early responses to S. epidermidis infections although is not essential for clearance of the infection (Cole et al., 2016).
Responses toward S. epidermidis can also occur independently of TLR-2, as it was shown in the models using TLR-2 KO mice (Bi et al., 2015). Other PRRs that may potentially be involved in S. epidermidis sensing are NOD-like receptors, as they recognize S. epidermidis-derived PDG (Natsuka et al., 2008). CD14, expressed mostly in monocytes and macrophages, is a TLR-2 co-receptor which may contribute to S. epidermidis recognition in some cell subsets (Hatakeyama et al., 2003). PSMs produced by S. epidermidis can be sensed by formyl peptide receptor 2 (FPR2/ALX) (Kretschmer et al., 2012, 2015), expressed in neutrophils and involved in their recruitment to the infection site (Rautenberg et al., 2011). To date, the contribution of these receptors in vivo has not been addressed.
Induction of Antimicrobial Peptides (AMPs)
Human AMPs are a heterogeneous group of amphipathic peptides, which may be subdivided depending on their structure and function. AMPs functions include rapid, direct killing of microbes and activation/modulation of immune responses, such as cell recruitment or chemokine production. One of the most effective early responses of the host to pathogenic insults is mediated through human β-defensins (hBD). In vitro experiments with keratinocytes or skin explants have shown that S. epidermidis or its culture supernatants can elicit high levels of hBD-2 and hBD-3 but not hBD-1 (Lai et al., 2010; Li et al., 2013; Ommori et al., 2013; Percoco et al., 2013; Park et al., 2014), and RNase7 and cathelicidin LL-37 in epithelial cells (Burgey et al., 2016). This AMP induction may be beneficial under healthy conditions to counteract more pathogenic species (Lai et al., 2010; Li et al., 2013) but can be also expected to contribute to defense in S. epidermidis superficial or ocular infections. Of relevance, some of them (hBD-2, hBD-3, LL-37 and human alpha defensin (HNP)-1) have been proven, to different extents, to be effective against S. epidermidis in vitro (Turner et al., 1998; Gordon et al., 2005; Huang et al., 2007; Dapunt et al., 2016b), although no data is available from in vivo studies. Nevertheless, the studies mentioned above showed some discrepancies in terms of AMP killing capacity, which could be explained by differences in strains used, as some of them may possess mechanisms against AMP. More relevant in the context of S. epidermidis DRI, other cell types including neutrophils and monocytes can produce AMPs. These AMPs will often be located in the phagolysosomes, where they can contribute to bacteria killing. Of interest, hBD-3, LL-37 and hepcidin 20, a liver-derived AMP, have been shown to reduce S. epidermidis attachment and/or biofilm formation in vitro (Hell et al., 2010; Zhu et al., 2013; Brancatisano et al., 2014). The mechanisms of action is currently unknown, although for hBD-3 a decrease in icaA and icaD expression and increase of icaR were associated with the observations (Zhu et al., 2013).
Phagocytosis/Killing by Neutrophils and Macrophages
Phagocytosis by neutrophils is one of the most important mechanisms for elimination of contaminating or infecting bacteria. Neutrophils migrate to the site of infection, following host signals (e.g., chemokines, AMPs) or sensing bacterial components as mentioned above. At the infection site, neutrophils will internalize opsonized bacteria forming a phagosome and, finally, bacteria will be destroyed in the phagolysosome by the action of reactive oxygen species (ROS), proteases and AMPs. An additional mechanism to kill bacteria has been described for neutrophils: the generation of neutrophil extracellular traps (NETs) or NETosis. Nuclear and mitochondrial DNA is released to the extracellular space to form NETs, which contain high local concentrations of intracellular antimicrobial proteins. Although literature is still limited, S. epidermidis biofilms have been shown to induce DNA release and NETosis in vitro (Meyle et al., 2012; Dapunt et al., 2016a). Macrophages are also able to phagocytose and destroy S. epidermidis (Riool et al., 2014) with similar mechanisms, and further present antigens to T cells. Phagocytosis of S. epidermidis by macrophages is enhanced following stimulation with IFN-γ in vitro (Magrys et al., 2015) and in vivo (Boelens et al., 2000a).
Phagocytes will also act against biofilms. It has been shown that neutrophils can bind to opsonized but also non-opsonized biofilms, partly by recognizing EPS (Meyle et al., 2012). Nevertheless, it is generally accepted that the biofilm mode of growth will protect bacteria from phagocytosis, despite some discrepancies in the literature that have been discussed elsewhere (Nguyen et al., 2017). Furthermore, biofilm mode of growth, most often studied in PIA-producing strains, has been shown to decrease killing efficiency in macrophages and neutrophils (Vuong et al., 2004c; Cerca et al., 2006; Kristian et al., 2008; Spiliopoulou et al., 2012).
Interesting observations were made when comparing the phagocytosis of S. epidermidis and S. aureus biofilms, with the latter being more likely infiltrated and engulfed (Guenther et al., 2009). However, although S. aureus was more likely phagocytosed, this does not always correlate with the capacity of neutrophils to kill the bacteria. In fact S. aureus has several mechanisms to avoid lysis by neutrophils and to persist intracellularly (Foster, 2005). S. epidermidis does not appear to possess similar mechanisms. However, some strains are killed less efficiently, potentially by having a low capacity to prime the oxidative response of neutrophils (Nilsdotter-Augustinsson et al., 2004), or as described before by their biofilm mode of growth. These observations, together with lower induction of neutrophil apoptosis, may lead to intracellular survival and could partially explain the low inflammatory nature and chronicity often associated with S. epidermidis infections.
Cytokine and Chemokine Secretion
Cytokines are a broad group of secreted proteins that play a role in intercellular communication, with a broad range of functions within the immune system as cell recruitment, differentiation and activation. Interleukins and other factors play an essential role in leukocyte communication and differentiation, while chemokines are mainly involved in cell recruitment. In vitro stimulation of peripheral blood mononuclear cells with different staphylococcal species showed a rapid release of pro-inflammatory cytokines such as IL-1β, IL-6, IL-12p70, or IFN-α (Megyeri et al., 2002). Of note, S. epidermidis induced lower levels of pro-inflammatory cytokines compared to S. aureus (Megyeri et al., 2002). Studies with monocytes/macrophages have also observed IL-6, tumor necrosis factor (TNF)-α and IL-1β release after S. epidermidis stimulation (Wilsson et al., 2008; Strunk et al., 2012). Laborel-Préneron et al. reported that stimulation of moDC with commensal S. epidermidis induced a more anti-inflammatory profile in contrast to stimulation with commensal strains of S. aureus, with high levels of IL-10 being a key differentiator. Nevertheless, pro-inflammatory cytokines such as IL-6 and TNF-α were also detected (Laborel-Preneron et al., 2015). Similar observations have been made from in vivo studies: IL-6, TNF-α, and IL-1β are typically observed in serum in the first hours post-challenge with live or inactivated S. epidermidis (Wakabayashi et al., 1991; Simojoki et al., 2011; Bi et al., 2015; Ferreirinha et al., 2016; Qin et al., 2017), or in tissue exudates/homogenates from experimental DRI models (Boelens et al., 2000b; Svensson et al., 2015). The regulatory cytokine IL-10 is also present in vivo (Ferreirinha et al., 2016) and it has been shown that S. epidermidis inoculation result in higher IL-10 levels compared to P. aeruginosa in an intradermal infection model (Bialecka et al., 2005). In a S. epidermidis DRI mouse model it was shown that IL-10 was involved in reducing infection-associated morbidity, with higher levels of pro-inflammatory cytokines and greater weight loss in IL-10 KO animals. Interestingly, bacterial counts were the same in both wild-type and KO strains, suggesting that IL-10 does not impact bacterial clearance (Gutierrez-Murgas et al., 2016). Overall, despite differences due to different S. epidermidis strains and its effect in different tissues, it can be hypothesized that lower induction of pro-inflammatory cytokines together with high IL-10 production, can contribute to the sub-acute nature of S. epidermidis infections.
Multiple chemokines are also released upon S. epidermidis infection. Secretion of IL-8, important for neutrophil recruitment, has been described in vitro and in the first hours post-infection in in vivo studies (Wakabayashi et al., 1991; Boelens et al., 2000b; Simojoki et al., 2011; Svensson et al., 2015). CXCL-1 and CXCL-2, mostly produced by macrophages (via TLR-2 recognition but also by other mechanisms), have also been observed in bacteraemia and peritonitis models (Strunk et al., 2010; Bi et al., 2015; Ferreirinha et al., 2016; Qin et al., 2017). Additionally, a murine peritonitis model revealed increasing levels of numerous chemokines upon challenge with S. epidermidis supernatants (Perks et al., 2016).
The aggregation and activation of platelets in the presence of bacteria was first described over 25 years ago (Usui et al., 1991) and yet the nature of this interaction has only recently been elucidated. Platelets and bacteria can interact in three ways: the indirect binding of bacteria to a plasma protein (which is a ligand of a platelet receptor), the direct recognition of bacteria by platelet receptors and the binding of secreted bacterial products to platelets (Hamzeh-Cognasse et al., 2015). Only the first type has been described for S. epidermidis, where the SdrG has been described to bind platelets in a fibrinogen and Ig-dependent manner; an interaction that leads to platelet aggregation (Brennan et al., 2009). S. aureus or Streptococcus have been shown to interact with platelets in other ways, which can lead to sepsis or thrombosis but also can play a role in internalization of bacteria by platelets or release of antimicrobial components and immunomodulatory factors (Hamzeh-Cognasse et al., 2015). Future studies will be required to elucidate if S. epidermidis-platelets interaction is limited to SdrG or if, like other bacteria, possess multiple mechanisms.
Adaptive Immune Response during Infection
Adaptive immunity refers to antigen-specific and long-lasting immune responses that are mediated by lymphocytes. Adaptive immunity can be broadly divided in cellular responses, represented by T helper (Th) and cytotoxic T lymphocytes, and humoral responses, represented by B lymphocytes and antibodies. Classically, extracellular bacterial infections have been shown to trigger mostly Th1 cell responses, but more recently Th17 responses have also been linked to the clearance of bacterial infections. Of relevance, an in vivo model using immunocompromised mice have shown a higher susceptibility for S. epidermidis DRI in mice lacking T cells or T and B cells (Vuong et al., 2008), highlighting a role for adaptive immune responses in infection clearance.
Arising from its status as a commensal microorganism, S. epidermidis is expected to elicit adaptive immune responses in humans from early in life. This has been proposed to be largely triggered by a pattern of transient self-resolving infections due to micro-invasions, rather than resulting from local response due to colonization (Brown et al., 2014), but the latter cannot be excluded. These life-long interactions will lead to the generation of an antibody repertoire and a set of memory T and B cells that may confer partial protection from infection. Generation of adaptive immune responses require the presentation of antigens to T cells by antigen presenting cells (APCs), primarily dendritic cells (DC), which will also contribute to T cell polarization. It has previously been shown that CD103+ skin-resident DC, upon interaction with commensal S. epidermidis, generates CD8+IL-17A+ T cells with the capacity to enhance protective responses in the skin (Naik et al., 2015). Upon infection, it can also be expected that certain DC subtypes, already present in the tissue or that will migrate there, will shape adaptive immune responses. Data available for S. epidermidis interaction with DC is very limited but it has been observed, in vitro and in vivo, that S. epidermidis can lead to DC activation with an increase in co-stimulatory molecules such as CD86 or CD80 and antigen presenting molecules such as major histocompatibility complex (MHC)-II (Stanislawska et al., 2005; Cerca et al., 2014; Laborel-Preneron et al., 2015; Franca et al., 2016). Studies describing cytokine secretion by DC stimulated with S. epidermidis (whole bacteria or its secreted proteins) have yielded somewhat inconsistent results. For example, IL-10 was not highly secreted when bone-marrow DC were stimulated with S. epidermidis (Cerca et al., 2014), but the stimulation of moDC with S. epidermidis secreted proteins led to high IL-10 secretion (Laborel-Preneron et al., 2015). The inconsistency between these reports may be due to the different sources of DC and stimuli used, which can lead to different outcomes by activating distinct pathways. The relevance of the stimuli is further highlighted in a series of experiments from Durantez et al. S. epidermidis PSM-derived peptides combined with ovalbumin were able to trigger cytotoxic T cell responses, however, this was only observed after those peptides were presented via APCs together with stimuli specific for TLR-3, TLR-7, and TLR-9 (Durantez et al., 2010). Further experiments are required to clarify the exact role of APCs and different DC subsets in priming and polarizing the T cell response.
With regards to humoral responses, antibodies against S. epidermidis proteins have been detected in serum and saliva of healthy individuals (Sadovskaya et al., 2007; Carvalhais et al., 2015), but levels are generally lower compared to S. epidermidis infected patients (Sadovskaya et al., 2007). Antibodies against biofilm components and cytoplasmic proteins have been found to be predominant (Carvalhais et al., 2015).
To assess the potential use of antibody titers in diagnosis of infection, serum antibody titters against Staphylococcal proteins have been measured in patients with S. aureus or S. epidermidis infections (such as wound infections, bacteremia or DRI). Recently, a multiplex antibody detection-based immunoassay was evaluated for the diagnosis of peri prosthetic joint infections (PJI). The assay included protein antigens from several strains: diverse Staphylococci, Streptococcus agalactiae and P. acnes (Marmor et al., 2016). The test showed a slightly lower sensitivity than C-reactive protein and erythrocyte sedimentation rate, however was able to diagnose around 50% of patients, which were culture positive but presented low systemic inflammation values (Marmor et al., 2016).
Another goal of humoral response studies is to identify immunogenic proteins, which can lead to development of therapeutic and/or prophylactic treatments. Studies employing 2D protein electrophoresis or phage display technology with the aim of identifying S. epidermidis immunogenic proteins have been performed in rabbits (Sellman et al., 2005) and humans (Pourmand et al., 2006). Sera of rabbits immunized with live S. epidermidis were used to detect relevant immunogens. Mice were then immunized with several selected proteins, five of whom (Na+/H+ antiporter, Acetyl-CoA C-acetyltransferase, lipoate ligase, cysteine synthase and alanine dehydrogenase) lead to a significant reduction of bacterial loads in a murine infection model (Sellman et al., 2005). Other proposed immunogenic proteins include AtlE, Staphylococcal conserved antigen B (ScaB), and GehD lipase, which elicited higher antibody titers in infected patients compared to non-infected subjects. Active immunization of mice with these antigens resulted in production of specific antibodies with in vitro opsonization capacity against S. epidermidis (Pourmand et al., 2006). An anti-SdrG antibody was shown to reduce mortality in a neonate bacteremia rat model and to decrease bacterial counts in a DRI (endocarditis) rabbit model (Vernachio et al., 2006), although it failed in a clinical trial to prevent late-onset sepsis in low-birth weight neonates (Schaffer and Lee, 2009). More recently it was shown that immunization with staphylococcal Major amidase (Atl-AM), a cell wall hydrolase present in some S. epidermidis and S. aureus strains, increases antibody levels against that protein in mice (Nair et al., 2015). In the same study, immunized animals challenged with a lethal intraperitoneal dose of S. epidermidis showed a better survival and lower bacterial counts in tissues compared to mock immunized animals (Nair et al., 2015). Additionally, immunized mice also presented higher levels of Th1 and Th2 cells, although it did not elucidate which responses were the most relevant for the increased survival. Immunizations with Aap or with antibodies against surface proteins have also been shown to reduce colonization in a murine DRI model by ultimately inhibiting biofilm formation (Shahrooei et al., 2012; Yan et al., 2014). Despite the fact that their efficacy against S. epidermidis infections has not been tested in vivo, antibodies against PNAG/PIA and phosphonate ABC transporter substrate binding protein (PhnD) have shown efficacy against S. epidermidis biofilm formation in vitro (Franca et al., 2013; Lam et al., 2014). A recent study focused on staphylococcal adhesion proteins, which contain long stretches of Sdr and are key virulence factors for S. epidermidis and also S. aureus. The study led to the discovery of two novel bacterial glycosyltransferases, SdgA and SdgB, which can modify all Sdr-proteins to protect them from cleavage by cathepsin G (a neutrophil protein). Neutralization of these enzymes may be the next opportunity for an effective anti-staphylococcal approach (Hazenbos et al., 2013). To date, all anti-staphylococcal antibodies tested against S. epidermidis and other CoNS in clinical trials (Altastaph, INH A-2, and Pagibaximab) have been found to be ineffective in reducing bacteremia in neonates (Patel and Kaufman, 2015). Although there is still much work to be done to fully understand effective immune responses against S. epidermidis, on-going research offers several candidates and strategies to develop new therapeutic products.
Additionally, there are also T cell-mediated immune responses to S. epidermidis although they are poorly characterized. Based on in vitro studies, it has been suggested that S. epidermidis opsonization with IgG promotes Th17 responses (den Dunnen et al., 2012), although the role of this phenomenon in vivo has not been shown. On the other hand, in an in vivo model of foreign-body infection, a beneficial effect of IFN-γ injections has been shown, suggesting a protective role of Th1 dominated responses in bacterial infections (Boelens et al., 2000a). Based on cytokines induced by S. epidermidis in the different studies (e.g., IL-6, IFN-γ, or IL-12), a Th1/Th17 polarization may be expected in such infections. This goes in line with the findings of Ferreirinha et al., who observed that injection of PNAG-producing S. epidermidis in mice lead to IFN-γ and IL-17A producing T cells (Ferreirinha et al., 2016). Also, as mentioned above, immunization of mice with Atl-AM led to an increase in Th1 and Th2 cells (Th17 cells were not evaluated on that study). Immunization also led to a higher survival; however, direct effect of T cell responses in that finding was not further addressed (Nair et al., 2015).
Bone System Interactions
The usual chronic nature of S. epidermidis osteomyelitis will eventually lead to an inflammatory environment within the bone system, which is of special relevance in the context of ODRIs. Bone as an organ is particularly sensitive to chronic inflammation, due to its continuous remodeling process that is influenced by different components of the immune system and inflammatory pathways (Redlich and Smolen, 2012). Due to their potent capacity to stimulate the formation and activity of bone resorbing osteoclasts, pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6 (Raisz, 1999; Kobayashi et al., 2000; Lam et al., 2000) are powerful drivers of osteolysis. Conversely, the function of the bone matrix-producing cells, osteoblasts, is also negatively affected by pro-inflammatory cytokines, such as TNF-α (Jilka et al., 1998; Gilbert et al., 2000, 2002) or IL-1β (Stashenko et al., 1987; Figure 4). Therefore, persistently elevated levels of pro-inflammatory cytokines in the local bone microenvironment frequently result in marked osteolysis, driven by enhanced osteoclast activity at the site of infection (Figure 4; Nair et al., 1996), which is likely compounded by a diminished capacity of osteoblasts to produce new bone matrix.
Figure 4. S. epidermidis direct and indirect effects on bone cells (osteoblasts and osteoclasts), leading to bone destruction.
Despite the importance of S. epidermidis as a causative agent in ODRI, relatively little information exists about the interactions of S. epidermidis with resident bone cells, in particular the molecular mechanisms underlying the bone loss observed in S. epidermidis-induced osteomyelitis. The production of cytokines by innate and/or adaptive immune cells in response to S. epidermidis is undoubtedly an important contributor to the enhanced bone resorption observed at the site of infection, however it is becoming apparent that the osteoblast itself may also directly contribute to the production of pro-inflammatory cytokines and therefore further perturb the balance of bone formation and resorption in favor of bone destruction. A recent study has shown the induction in vitro of IL-6 by primary human osteoblasts stimulated with S. epidermidis (Dapunt et al., 2016b). S. epidermidis infection also induced chemokines, such as IL-8/CXCL8 and CCL2/MCP-1, suggesting that osteoblasts may be capable of further recruiting immune cells following an encounter with S. epidermidis. Interestingly, the authors also demonstrated that osteoblasts were activated not only by the planktonic form of S. epidermidis but also by components of S. epidermidis biofilms. This suggests that, rather than the relatively simplistic view of the osteoblast for producing bone matrix and regulating osteoclast activity, osteoblasts may also serve an important role as sensors and initiators of immune responses directed against bacteria resident in the local bone microenvironment.
Additionally, in vitro studies have observed a decrease in osteoblast viability when co-cultured with S. epidermidis (Lee et al., 2010; Zaatreh et al., 2016). S. epidermidis products (resulting from washing bacteria) have been suggested to induce bone destruction as they increased calcium release from murine bones in vitro (Meghji et al., 1997). This is in stark contrast to S. aureus, which has been extensively studied in this context and is capable of influencing the behavior of both osteoblasts and osteoclasts. For example, S. aureus has been demonstrated to induce TRAIL-dependent apoptosis in osteoblasts (Tucker et al., 2000; Alexander et al., 2001, 2003; Young et al., 2011) and can stimulate expression of osteolytic factors (Somayaji et al., 2008) or reduce the expression of its inhibitors (Young et al., 2011), exacerbating the osteolytic effect. Furthermore, specific bacterial proteins have been identified as responsible for some of these effects on osteoblasts such as S. aureus protein A, which has been demonstrated to bind directly to TNF receptor 1, resulting in an inhibitory effect on proliferation, the induction of apoptosis, and the stimulation of RANKL expression (Claro et al., 2011, 2013).
Regarding the effects of bacterial infection on osteoclasts, a number of studies have reported the effects of inactivated S. aureus, or specific S. aureus components, for affecting osteoclast formation and/or activity (Yang et al., 2009; Pietrocola et al., 2011; Kishimoto et al., 2012; Kim et al., 2013). Conversely, staphylococcal LTA inhibits osteoclastogenesis through stimulation of TLR-2 activity (Yang et al., 2009). Such conflicting data strongly argues for the use of (preferably live) intact bacteria in such osteoclastogenesis assays rather than purified bacterial components. When the effect of intact bacteria on osteoclastogenesis was recently investigated, S. aureus was demonstrated to have both direct and indirect stimulatory effects on osteoclasts in vitro (Trouillet-Assant et al., 2015). By inducing activation of macrophages and thereby stimulating the production of pro-inflammatory cytokines, S. aureus indirectly enhanced the formation of osteoclasts from precursor cells. Additionally, S. aureus could also directly infect mature osteoclasts, resulting in increased cell fusion and enhanced bone resorbing capacity. Much less is known regarding direct interaction of S. epidermidis and osteoclasts, although it is expected that induction of pro-inflammatory cytokines will enhance bone destruction in similar ways.
Given the multitude of different effects of S. aureus on osteoblast and osteoclast function, it is likely that S. epidermidis can also negatively affect the capacity of osteoblasts to produce bone matrix and/or enhance osteoclast formation and function, although much further work is necessary to clarify if this is indeed the case.
Lastly, the interaction of S. epidermidis with bone cells could provide a location where bacteria can persist and prolong ODRIs. Both S. aureus and S. epidermidis are capable of invading osteoblasts in vitro (Ahmed et al., 2001; Khalil et al., 2007), however the mechanism underlying this phenomenon appears to differ between these two species. S. aureus requires binding to the ECM protein fibronectin, mediated by α5β1 integrin (Sinha et al., 1999), whereas S. epidermidis internalization by osteoblasts is not affected by interfering with fibronectin binding or blocking, suggesting a different mechanism (Khalil et al., 2007). This is supported by the findings of a recent study that reported SdrG mediates the binding of S. epidermidis to osteoblasts in vitro, an effect likely mediated through SdrG binding to αVβ3 integrin (Claro et al., 2015). However, this immune evasion mechanism may be of more importance for S. aureus rather than S. epidermidis per se, since the capacity of S. epidermidis for invading osteoblasts in vitro does not appear to differ between commensal strains and clinical isolates of S. epidermidis obtained from infected orthopedic devices (Valour et al., 2013). This is reinforced by a recent in vitro study demonstrating that S. epidermidis as well as other opportunistic pathogens such as S. lugdunensis and Enterococcus faecalis were incompetent at being internalized by MG63 human osteoblastic cells, being internalized at a level approximately three orders of magnitude lower than that observed with S. aureus (Campoccia et al., 2015). Osteoclasts are also able to internalize, at least, S. aureus. Given the inherent phagocytic capacity of osteoclasts, it may be that internalization of S. aureus by osteoclasts relies on such a phagocytic mechanism of uptake. This raises the possibility that S. epidermidis may also be the object of uptake by osteoclasts. Together with the previously stated ability of S. epidermidis to bind to αVβ3 integrin, which is highly expressed by osteoclasts (Quinn et al., 1991), this further suggests that S. epidermidis may bind to and be internalized by osteoclasts, although this and the subsequent phenotypical changes resulting from such an interaction requires to be validated experimentally. Taken together, this suggests that while the persistence of orthopedic implant-associated S. aureus infections in vivo may well stem from its enhanced ability to invade osteoblasts, and potentially osteoclasts, other mechanisms, such as biofilm formation, may underlie the persistence of S. epidermidis in implant-related infection.
Finally, the integration of immune responses within the bone system in the context of S. epidermidis infection has been largely unexplored. The number of models described for S. epidermidis bone infection is limited (Table 1) and none have really focused on host immune responses. Most of the data available is based on S. aureus models, where a combination of Th1/Th17 responses have been observed (Prabhakara et al., 2011a; Rochford et al., 2016), although it is not clear if this response is beneficial or detrimental to the host as no bacterial clearance was achieved (Prabhakara et al., 2011b; Jensen et al., 2015). The observation that anti-IL-12p40 conferred protection in S. aureus infected C57BL/6 mice supported the hypothesis that skewed Th1/Th17 responses may be harmful (Prabhakara et al., 2011b), as IL-12/IL-23p40 plays a role in polarization of these cell types. This observation, however, could be due to a decrease in myeloid-derived suppressor cells (MDSC) that otherwise would impair immune responses in the vicinity of an implant, as described by Heim et al. (2015). The use of different murine strains, inoculum dose and models are factors contributing to the disparity in the available data. Furthermore, the differences between S. aureus and S. epidermidis are quite significant, and so further work focused on S. epidermidis is required to provide a proper understanding of adaptive immune responses to S. epidermidis bone infection.
Summary and Outlook
S. epidermidis is a commensal microorganism adapted for the colonization of human skin. In healthy individuals, S. epidermidis can provide several benefits by competing with pathogenic species or by modulating the immune system. Induction of tolerance has been demonstrated recently in murine models although similar mechanisms remain to be proven in humans. The great advances in “omics” are providing enormous amounts of data about cell/tissue behavior and also about human microbiome (from transcriptome to metabolome). The application and integration of this data for S. epidermidis commensalism will provide a much better understanding of the roles of S. epidermidis in health and also in certain skin diseases, such as atopic dermatitis or psoriasis.
Upon a transition to a pathogenic interaction with the host, as occurs in DRI, the same mechanisms that allow S. epidermidis to reside in human skin and mucosal tissues allow adhesion and biofilm formation upon the implanted device. Adhesion to host proteins and biofilm formation are thought to be the main S. epidermidis pathogenic mechanisms. For this reason, the development of antimicrobial surfaces and therapies targeting biofilm are areas which are expected to be in development in the coming years. In the face of high antibiotic resistance, these technologies may need to consider alternative antimicrobial agents.
Finally, there remains a lack of understanding of immune responses to S. epidermidis infections. S. epidermidis seems to trigger low levels of pro-inflammatory cytokines secretion and high levels of IL-10, which may contribute to the sub-acute nature and persistence of the infection. As yet, adaptive immune responses to the bacterium remain poorly described and are an area which may provide significant new discoveries in the coming years.
MSB, LGH, KT, BS, MM, and TFM wrote the manuscript and approved its final version. MSB, and LGH were involved in figures preparation. TFM, LO, and RGR corrected and critically evaluated the manuscript.
This work was supported by the AO Trauma (grant AR2011_08).
Conflict of Interest Statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Aae, Autolysin/adhesion from S. epidermidis; Aap, Accumulation associated protein; AMPs, Antimicrobial peptides; APC, Antigen-presenting cell; AtlE, Autolysin; Bhp, Biofilm associated homolog protein; CoNS, Coagulase-negative staphylococcus; CWA, Cell-wall-anchored; DC, Dendritic cells; DRI, Device-related infection; ECM, Extracellular matrix; eDNA, Extracellular DNA; Embp, Extracellular matrix-binding protein; EPS, Extracellular polymeric substances; FPR2, Formyl peptide receptor 2; IFN, Interferon; IL, Interleukin; KO, Knock-out; LTA, Lipoteichoic acid; moDC, Monocyte-derived dendritic cells; MRSE, Methicillin resistant S. epidermidis; MSCRAMMs, Microbial surface components recognizing adhesive matrix molecules; ODRIs, Orthopedic device-related infections; PDG, Peptidoglycan; PIA, Polysaccharide intercellular adhesin; PGA, Poly-γ-glutamic acid; PSMs, Phenol-soluble modulins; RANKL, Receptor activator of NFκB ligand; ROS, Reactive oxygen species; Sdr, Serine-aspartate repeat protein; SCCmec, Staphylococcal cassette chromosome mec; Ses, S. epidermidis surface protein; SCV, Small colony variant; SSP, Staphylococcal surface protein; TNF-α, Tumor necrosis factor alpha; Th, T helper; TLR, Toll-like receptor; WTA, Wall teichoic acids.
Ahmed, S., Meghji, S., Williams, R. J., Henderson, B., Brock, J. H., and Nair, S. P. (2001). Staphylococcus aureus fibronectin binding proteins are essential for internalization by osteoblasts but do not account for differences in intracellular levels of bacteria. Infect. Immun. 69, 2872–2877. doi: 10.1128/IAI.69.5.2872-2877.2001
Ahtinen, H., Kulkova, J., Lindholm, L., Eerola, E., Hakanen, A. J., Moritz, N., et al. (2014). (68)Ga-DOTA-Siglec-9 PET/CT imaging of peri-implant tissue responses and staphylococcal infections. EJNMMI Res. 4:45. doi: 10.1186/s13550-014-0045-3
Alexander, E. H., Bento, J. L., Hughes, F. M. Jr., Marriott, I., Hudson, M. C., and Bost, K. L. (2001). Staphylococcus aureus and Salmonella enterica serovar Dublin induce tumor necrosis factor-related apoptosis-inducing ligand expression by normal mouse and human osteoblasts. Infect. Immun. 69, 1581–1586. doi: 10.1128/IAI.69.3.1581-1586.2001
Alexander, E. H., Rivera, F. A., Marriott, I., Anguita, J., Bost, K. L., and Hudson, M. C. (2003). Staphylococcus aureus–induced tumor necrosis factor–related apoptosis–inducing ligand expression mediates apoptosis and caspase-8 activation in infected osteoblasts. BMC Microbiol. 3:5. doi: 10.1186/1471-2180-3-5
Al-Ishaq, R., Armstrong, J., Gregory, M., O'Hara, M., Phiri, K., Harris, L. G., et al. (2015). Effects of polysaccharide intercellular adhesin (PIA) in an ex vivo model of whole blood killing and in prosthetic joint infection (PJI): a role for C5a. Int. J. Med. Microbiol. 305, 948–956. doi: 10.1016/j.ijmm.2015.08.005
Allgaier, H., Jung, G., Werner, R. G., Schneider, U., and Zahner, H. (1986). Epidermin: sequencing of a heterodetic tetracyclic 21-peptide amide antibiotic. Eur. J. Biochem. 160, 9–22. doi: 10.1111/j.1432-1033.1986.tb09933.x
An, Y. H., Bradley, J., Powers, D. L., and Friedman, R. J. (1997). The prevention of prosthetic infection using a cross-linked albumin coating in a rabbit model. J. Bone Joint Surg. Br. 79, 816–819. doi: 10.1302/0301-620X.79B5.7228
Arciola, C. R., Bustanji, Y., Conti, M., Campoccia, D., Baldassarri, L., Samori, B., et al. (2003). Staphylococcus epidermidis-fibronectin binding and its inhibition by heparin. Biomaterials 24, 3013–3019. doi: 10.1016/S0142-9612(03)00133-9
Arrecubieta, C., Lee, M.-H., Macey, A., Foster, T. J., and Lowy, F. D. (2007). SdrF, a Staphylococcus epidermidis surface protein, binds type I collagen. J. Biol. Chem. 282, 18767–18776. doi: 10.1074/jbc.M610940200
Baier, R. E., Meyer, A. E., Natiella, J. R., Natiella, R. R., and Carter, J. M. (1984). Surface properties determine bioadhesive outcomes: methods and results. J. Biomed. Mater. Res. 18, 327–355. doi: 10.1002/jbm.820180404
Bastos, M. C., Ceotto, H., Coelho, M. L., and Nascimento, J. S. (2009). Staphylococcal antimicrobial peptides: relevant properties and potential biotechnological applications. Curr. Pharm. Biotechnol. 10, 38–61. doi: 10.2174/138920109787048580
Bennallack, P. R., Burt, S. R., Heder, M. J., Robison, R. A., and Griffitts, J. S. (2014). Characterization of a novel plasmid-borne thiopeptide gene cluster in Staphylococcus epidermidis strain 115. J. Bacteriol. 196, 4344–4350. doi: 10.1128/JB.02243-14
Bi, D., Qiao, L., Bergelson, I., Ek, C. J., Duan, L., Zhang, X., et al. (2015). Staphylococcus epidermidis bacteremia induces brain injury in neonatal mice via toll-like receptor 2-dependent and -independent pathways. J. Infect. Dis. 212, 1480–1490. doi: 10.1093/infdis/jiv231
Bialecka, A., Mak, M., Biedron, R., Bobek, M., Kasprowicz, A., and Marcinkiewicz, J. (2005). Different pro-inflammatory and immunogenic potentials of Propionibacterium acnes and Staphylococcus epidermidis: implications for chronic inflammatory acne. Arch. Immunol. Ther. Exp. (Warsz). 53, 79–85.
Bjorkqvist, M., Liljedahl, M., Zimmermann, J., Schollin, J., and Soderquist, B. (2010). Colonization pattern of coagulase-negative staphylococci in preterm neonates and the relation to bacteremia. Eur. J. Clin. Microbiol. Infect. Dis. 29, 1085–1093. doi: 10.1007/s10096-010-0966-3
Boelens, J. J., van der Poll, T., Dankert, J., and Zaat, S. A. (2000a). Interferon-gamma protects against biomaterial-associated Staphylococcus epidermidis infection in mice. J. Infect. Dis. 181, 1167–1171. doi: 10.1086/315344
Boelens, J. J., van der Poll, T., Zaat, S. A., Murk, J. L., Weening, J. J., and Dankert, J. (2000b). Interleukin-1 receptor type I gene-deficient mice are less susceptible to Staphylococcus epidermidis biomaterial-associated infection than are wild-type mice. Infect. Immun. 68, 6924–6931. doi: 10.1128/IAI.68.12.6924-6931.2000
Bowden, M. G., Chen, W., Singvall, J., Xu, Y., Peacock, S. J., Valtulina, V., et al. (2005). Identification and preliminary characterization of cell-wall-anchored proteins of Staphylococcus epidermidis. Microbiology 151(Pt 5), 1453–1464. doi: 10.1099/mic.0.27534-0
Bowden, M. G., Visai, L., Longshaw, C. M., Holland, K. T., Speziale, P., and Hook, M. (2002). Is the GehD lipase from Staphylococcus epidermidis a collagen binding adhesin? J. Biol. Chem. 277, 43017–43023. doi: 10.1074/jbc.M207921200
Brancatisano, F. L., Maisetta, G., Di Luca, M., Esin, S., Bottai, D., Bizzarri, R., et al. (2014). Inhibitory effect of the human liver-derived antimicrobial peptide hepcidin 20 on biofilms of polysaccharide intercellular adhesin (PIA)-positive and PIA-negative strains of Staphylococcus epidermidis. Biofouling 30, 435–446. doi: 10.1080/08927014.2014.888062
Brennan, M. P., Loughman, A., Devocelle, M., Arasu, S., Chubb, A. J., Foster, T. J., et al. (2009). Elucidating the role of Staphylococcus epidermidis serine-aspartate repeat protein G in platelet activation. J. Thromb. Haemost. 7, 1364–1372. doi: 10.1111/j.1538-7836.2009.03495.x
Brown, A. F., Leech, J. M., Rogers, T. R., and McLoughlin, R. M. (2014). Staphylococcus aureus colonization: modulation of host immune response and impact on human vaccine design. Front. Immunol. 4:507. doi: 10.3389/fimmu.2013.00507
Burgey, C., Kern, W. V., Romer, W., and Rieg, S. (2016). Differential induction of innate defense antimicrobial peptides in primary nasal epithelial cells upon stimulation with inflammatory cytokines, Th17 cytokines or bacterial conditioned medium from Staphylococcus aureus isolates. Microb. Pathog. 90, 69–77. doi: 10.1016/j.micpath.2015.11.023
Campoccia, D., Testoni, F., Ravaioli, S., Cangini, I., Maso, A., Speziale, P., et al. (2015). Orthopedic implant-infections. Incompetence of Staphylococcus epidermidis, Staphylococcus lugdunensis and Enterococcus faecalis to invade osteoblasts. J. Biomed. Mater. Res. A. 104, 788–801. doi: 10.1002/jbm.a.35564
Carvalhais, V., Amado, F., Cerveira, F., Ferreira, R., Vilanova, M., Cerca, N., et al. (2015). Immunoreactive pattern of Staphylococcus epidermidis biofilm against human whole saliva. Electrophoresis 36, 1228–1233. doi: 10.1002/elps.201500043
Cerca, F., Andrade, F., Franca, A., Andrade, E. B., Ribeiro, A., Almeida, A. A., et al. (2011). Staphylococcus epidermidis biofilms with higher proportions of dormant bacteria induce a lower activation of murine macrophages. J. Med. Microbiol. 60(Pt 12), 1717–1724. doi: 10.1099/jmm.0.031922-0
Cerca, F., Franca, A., Perez-Cabezas, B., Carvalhais, V., Ribeiro, A., Azeredo, J., et al. (2014). Dormant bacteria within Staphylococcus epidermidis biofilms have low inflammatory properties and maintain tolerance to vancomycin and penicillin after entering planktonic growth. J. Med. Microbiol. 63(Pt 10), 1274–1283. doi: 10.1099/jmm.0.073163-0
Cerca, N., Jefferson, K. K., Oliveira, R., Pier, G. B., and Azeredo, J. (2006). Comparative antibody-mediated phagocytosis of Staphylococcus epidermidis cells grown in a biofilm or in the planktonic state. Infect. Immun. 74, 4849–4855. doi: 10.1128/IAI.00230-06
Chambers, H. F., Hartman, B. J., and Tomasz, A. (1985). Increased amounts of a novel penicillin-binding protein in a strain of methicillin-resistant Staphylococcus aureus exposed to nafcillin. J. Clin. Invest. 76, 325–331. doi: 10.1172/JCI111965
Cherifi, S., Byl, B., Deplano, A., Nonhoff, C., Denis, O., and Hallin, M. (2013). Comparative epidemiology of Staphylococcus epidermidis isolates from patients with catheter-related bacteremia and from healthy volunteers. J. Clin. Microbiol. 51, 1541–1547. doi: 10.1128/JCM.03378-12
Cheung, G. Y., Rigby, K., Wang, R., Queck, S. Y., Braughton, K. R., Whitney, A. R., et al. (2010). Staphylococcus epidermidis strategies to avoid killing by human neutrophils. PLoS Pathog. 6:e1001133. doi: 10.1371/journal.ppat.1001133
Chokr, A., Leterme, D., Watier, D., and Jabbouri, S. (2007). Neither the presence of ica locus, nor in vitro-biofilm formation ability is a crucial parameter for some Staphylococcus epidermidis strains to maintain an infection in a guinea pig tissue cage model. Microb. Pathog. 42, 94–97. doi: 10.1016/j.micpath.2006.09.001
Christensen, G. J., Scholz, C. F., Enghild, J., Rohde, H., Kilian, M., Thurmer, A., et al. (2016). Antagonism between Staphylococcus epidermidis and Propionibacterium acnes and its genomic basis. BMC Genomics 17:152. doi: 10.1186/s12864-016-2489-5
Christner, M., Franke, G. C., Schommer, N. N., Wend, T. Wegert, K., Pehle, P., et al. (2010). The giant extracellular matrix-binding protein of Staphylococcus epidermidis mediates biofilm accumulation and attachment to fibronectin. Mol. Microbiol. 75, 187–207. doi: 10.1111/j.1365-2958.2009.06981.x
Christner, M., Heinze, C., Busch, M., Franke, G., Hentschke, M., Bayard Duhring, S., et al. (2012). sarA negatively regulates Staphylococcus epidermidis biofilm formation by modulating expression of 1 MDa extracellular matrix binding protein and autolysis-dependent release of eDNA. Mol. Microbiol. 86, 394–410. doi: 10.1111/j.1365-2958.2012.08203.x
Chugh, T. D., Burns, G. J., Shuhaiber, H. J., and Bahr, G. M. (1990). Adherence of Staphylococcus epidermidis to fibrin-platelet clots in vitro mediated by lipoteichoic acid. Infect. Immun. 58, 315–319.
Claro, T., Kavanagh, N., Foster, T. J., O'Brien, F. J., and Kerrigan, S. W. (2015). Staphylococcus epidermidis serine–aspartate repeat protein G (SdrG) binds to osteoblast integrin alpha V beta 3. Microbes Infect. 17, 395–401. doi: 10.1016/j.micinf.2015.02.003
Claro, T., Widaa, A., McDonnell, C., Foster, T. J., O'Brien, F. J., and Kerrigan, S. W. (2013). Staphylococcus aureus protein A binding to osteoblast tumour necrosis factor receptor 1 results in activation of nuclear factor kappa B and release of interleukin-6 in bone infection. Microbiology 159(Pt 1), 147–154. doi: 10.1099/mic.0.063016-0
Claro, T., Widaa, A., O'Seaghdha, M., Miajlovic, H., Foster, T. J., O'Brien, F. J., et al. (2011). Staphylococcus aureus protein A binds to osteoblasts and triggers signals that weaken bone in osteomyelitis. PLoS ONE 6:e18748. doi: 10.1371/journal.pone.0018748
Cogen, A. L., Yamasaki, K., Muto, J., Sanchez, K. M., Crotty Alexander, L., Tanios, J., et al. (2010a). Staphylococcus epidermidis antimicrobial delta-toxin (phenol-soluble modulin-gamma) cooperates with host antimicrobial peptides to kill group A Streptococcus. PLoS ONE 5:e8557. doi: 10.1371/journal.pone.0008557
Cogen, A. L., Yamasaki, K., Sanchez, K. M., Dorschner, R. A., Lai, Y., MacLeod, D. T., et al. (2010b). Selective antimicrobial action is provided by phenol-soluble modulins derived from Staphylococcus epidermidis, a normal resident of the skin. J. Invest. Dermatol. 130, 192–200. doi: 10.1038/jid.2009.243
Cole, L. E., Zhang, J., Kesselly, A., Anosova, N. G., Lam, H., Kleanthous, H., et al. (2016). Limitations of murine models for assessment of antibody-mediated therapies or vaccine candidates against Staphylococcus epidermidis bloodstream infection. Infect. Immun. 84, 1143–1149. doi: 10.1128/IAI.01472-15
Collado, M. C., Rautava, S., Aakko, J., Isolauri, E., and Salminen, S. (2016). Human gut colonisation may be initiated in utero by distinct microbial communities in the placenta and amniotic fluid. Sci. Rep. 6:23129. doi: 10.1038/srep23129
Costerton, J. W., Post, J. C., Ehrlich, G. D., Hu, F. Z., Kreft, R., Nistico, L., et al. (2011). New methods for the detection of orthopedic and other biofilm infections. FEMS Immunol. Med. Microbiol. 61, 133–140. doi: 10.1111/j.1574-695X.2010.00766.x
Dapunt, U., Gaida, M. M., Meyle, E., Prior, B., and Hansch, G. M. (2016a). Activation of phagocytic cells by Staphylococcus epidermidis biofilms: effects of extracellular matrix proteins and the bacterial stress protein GroEL on netosis and MRP-14 release. Pathog. Dis. 74:ftw035. doi: 10.1093/femspd/ftw035
Dapunt, U., Giese, T., Stegmaier, S., Moghaddam, A., and Hansch, G. M. (2016b). The osteoblast as an inflammatory cell: production of cytokines in response to bacteria and components of bacterial biofilms. BMC Musculoskelet. Disord. 17:243. doi: 10.1186/s12891-016-1091-y
Dapunt, U., Spranger, O., Gantz, S., Burckhardt, I., Zimmermann, S., Schmidmaier, G., et al. (2015). Are atrophic long-bone nonunions associated with low-grade infections? Ther. Clin. Risk Manag. 11, 1843–1852. doi: 10.2147/TCRM.S91532
Del Pozo, J. L., Rouse, M. S., Euba, G., Kang, C. I., Mandrekar, J. N., Steckelberg, J. M., et al. (2009). The electricidal effect is active in an experimental model of Staphylococcus epidermidis chronic foreign body osteomyelitis. Antimicrob. Agents Chemother. 53, 4064–4068. doi: 10.1128/AAC.00432-09
den Dunnen, J., Vogelpoel, L. T., Wypych, T., Muller, F. J., de Boer, L., Kuijpers, T. W., et al. (2012). IgG opsonization of bacteria promotes Th17 responses via synergy between TLRs and FcgammaRIIa in human dendritic cells. Blood 120, 112–121. doi: 10.1182/blood-2011-12-399931
Dhople, V. M., and Nagaraj, R. (1993). Delta-toxin, unlike melittin, has only hemolytic activity and no antimicrobial activity: rationalization of this specific biological activity. Biosci. Rep. 13, 245–250. doi: 10.1007/BF01123506
Diekema, D. J., Pfaller, M. A., Schmitz, F. J., Smayevsky, J., Bell, J., Jones, R. N., et al. (2001). Survey of infections due to Staphylococcus species: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, Latin America, Europe, and the Western Pacific region for the SENTRY Antimicrobial Surveillance Program, 1997–1999. Clin. Infect. Dis. 32(Suppl. 2), S114–132. doi: 10.1086/320184
Dominguez-Bello, M. G., Costello, E. K., Contreras, M., Magris, M., Hidalgo, G., Fierer, N., et al. (2010). Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc. Natl. Acad. Sci. U.S.A. 107, 11971–11975. doi: 10.1073/pnas.1002601107
Durantez, M., Fayolle, C., Casares, N., Belsue, V., Riezu-Boj, J. I., Sarobe, P., et al. (2010). Tumor therapy in mice by using a tumor antigen linked to modulin peptides from Staphylococcus epidermidis. Vaccine 28, 7146–7154. doi: 10.1016/j.vaccine.2010.08.070
Ekkelenkamp, M. B., Hanssen, M., Danny Hsu, S. T., de Jong, A., Milatovic, D., Verhoef, J., et al. (2005). Isolation and structural characterization of epilancin 15X, a novel lantibiotic from a clinical strain of Staphylococcus epidermidis. FEBS Lett. 579, 1917–1922. doi: 10.1016/j.febslet.2005.01.083
Farina, N., Samudio, M., Carpinelli, L., Nentwich, M. M., and de Kaspar, H. M. (2016). Methicillin resistance and biofilm production of Staphylococcus epidermidis isolates from infectious and normal flora conjunctiva. Int. Ophthalmol. 37, 819–825. doi: 10.1007/s10792-016-0339-8
Ferreirinha, P., Perez-Cabezas, B., Correia, A., Miyazawa, B., Franca, A., Carvalhais, V., et al. (2016). Poly-N-acetylglucosamine production by Staphylococcus epidermidis cells increases their in vivo proinflammatory effect. Infect. Immun. 84, 2933–2943. doi: 10.1128/IAI.00290-16
Franca, A., Perez-Cabezas, B., Correia, A., Pier, G. B., Cerca, N., and Vilanova, M. (2016). Staphylococcus epidermidis Biofilm-released cells induce a prompt and more marked in vivo inflammatory-type response than planktonic or biofilm cells. Front. Microbiol. 7:1530. doi: 10.3389/fmicb.2016.01530
Franca, A., Vilanova, M., Cerca, N., and Pier, G. B. (2013). Monoclonal antibody raised against PNAG has variable effects on static S. epidermidis biofilm accumulation in vitro. Int. J. Biol. Sci. 9, 518–520. doi: 10.7150/ijbs.6102
Frank, D. N., Feazel, L. M., Bessesen, M. T., Price, C. S., Janoff, E. N., and Pace, N. R. (2010). The human nasal microbiota and Staphylococcus aureus carriage. PLoS ONE 5:e10598. doi: 10.1371/journal.pone.0010598
Gilbert, L., He, X., Farmer, P., Boden, S., Kozlowski, M., Rubin, J., et al. (2000). Inhibition of osteoblast differentiation by tumor necrosis factor-alpha. Endocrinology 141, 3956–3964. doi: 10.1210/endo.141.11.7739
Gilbert, L., He, X., Farmer, P., Rubin, J., Drissi, H., van Wijnen, A. J., et al. (2002). Expression of the osteoblast differentiation factor RUNX2 (Cbfa1/AML3/Pebp2alpha A) is inhibited by tumor necrosis factor-alpha. J. Biol. Chem. 277, 2695–2701. doi: 10.1074/jbc.M106339200
Gill, S. R., Fouts, D. E., Archer, G. L., Mongodin, E. F., Deboy, R. T., Ravel, J., et al. (2005). Insights on evolution of virulence and resistance from the complete genome analysis of an early methicillin-resistant Staphylococcus aureus strain and a biofilm-producing methicillin-resistant Staphylococcus epidermidis strain. J. Bacteriol. 187, 2426–2438. doi: 10.1128/JB.187.7.2426-2438.2005
Gordon, Y. J., Huang, L. C., Romanowski, E. G., Yates, K. A., Proske, R. J., and McDermott, A. M. (2005). Human cathelicidin (LL-37), a multifunctional peptide, is expressed by ocular surface epithelia and has potent antibacterial and antiviral activity. Curr. Eye Res. 30, 385–394. doi: 10.1080/02713680590934111
Grice, E. A., Kong, H. H., Conlan, S., Deming, C. B., Davis, J., Young, A. C., et al. (2009). Topographical and temporal diversity of the human skin microbiome. Science 324, 1190–1192. doi: 10.1126/science.1171700
Guenther, F., Stroh, P., Wagner, C., Obst, U., and Hansch, G. M. (2009). Phagocytosis of staphylococci biofilms by polymorphonuclear neutrophils: S. aureus and S. epidermidis differ with regard to their susceptibility towards the host defense. Int. J. Artif. Organs 32, 565–573.
Gutierrez-Murgas, Y. M., Skar, G., Ramirez, D., Beaver, M., and Snowden, J. N. (2016). IL-10 plays an important role in the control of inflammation but not in the bacterial burden in S. epidermidis CNS catheter infection. J. Neuroinflammation 13:271. doi: 10.1186/s12974-016-0741-1
Hajjar, A. M., O'Mahony, D. S., Ozinsky, A., Underhill, D. M., Aderem, A., Klebanoff, S. J., et al. (2001). Cutting edge: functional interactions between toll-like receptor (TLR) 2 and TLR1 or TLR6 in response to phenol-soluble modulin. J. Immunol. 166, 15–19. doi: 10.4049/jimmunol.166.1.15
Hamzeh-Cognasse, H., Damien, P., Chabert, A., Pozzetto, B., Cognasse, F., and Garraud, O. (2015). Platelets and infections–complex interactions with bacteria. Front. Immunol. 6:82. doi: 10.3389/fimmu.2015.00082
Harris, L. G., Murray, S., Pascoe, B., Bray, J., Meric, G., Magerios, L., et al. (2016). Biofilm Morphotypes and Population Structure among Staphylococcus epidermidis from Commensal and Clinical Samples. PLoS ONE 11:e0151240. doi: 10.1371/journal.pone.0151240
Hartford, O., O'Brien, L., Schofield, K., Wells, J., and Foster, T. J. (2001). The Fbe (SdrG) protein of Staphylococcus epidermidis HB promotes bacterial adherence to fibrinogen. Microbiology 147, 2545–2552. doi: 10.1099/00221287-147-9-2545
Hassan, M., Kjos, M., Nes, I. F., Diep, D. B., and Lotfipour, F. (2012). Natural antimicrobial peptides from bacteria: characteristics and potential applications to fight against antibiotic resistance. J. Appl. Microbiol. 113, 723–736. doi: 10.1111/j.1365-2672.2012.05338.x
Hatakeyama, J., Tamai, R., Sugiyama, A., Akashi, S., Sugawara, S., and Takada, H. (2003). Contrasting responses of human gingival and periodontal ligament fibroblasts to bacterial cell-surface components through the CD14/Toll-like receptor system. Oral Microbiol. Immunol. 18, 14–23. doi: 10.1034/j.1399-302X.2003.180103.x
Hazenbos, W. L., Kajihara, K. K., Vandlen, R., Morisaki, J. H., Lehar, S. M., Kwakkenbos, M. J., et al. (2013). Novel staphylococcal glycosyltransferases SdgA and SdgB mediate immunogenicity and protection of virulence-associated cell wall proteins. PLoS Pathog. 9:e1003653. doi: 10.1371/journal.ppat.1003653
Heilmann, C., Hussain, M., Peters, G., and Gotz, F. (1997). Evidence for autolysin-mediated primary attachment of Staphylococcus epidermidis to a polystyrene surface. Mol. Microbiol. 24, 1013–1024. doi: 10.1046/j.1365-2958.1997.4101774.x
Heilmann, C., Schweitzer, O., Gerke, C., Vanittanakom, N., Mack, D., and Gotz, F. (1996). Molecular basis of intercellular adhesion in the biofilm-forming Staphylococcus epidermidis. Mol. Microbiol. 20, 1083–1091. doi: 10.1111/j.1365-2958.1996.tb02548.x
Heilmann, C., Thumm, G., Chhatwal, G. S., Hartleib, J., Uekotter, A., and Peters, G. (2003). Identification and characterization of a novel autolysin (Aae) with adhesive properties from Staphylococcus epidermidis. Microbiology 149, 2769–2778. doi: 10.1099/mic.0.26527-0
Heim, C. E., Vidlak, D., Scherr, T. D., Hartman, C. W., Garvin, K. L., and Kielian, T. (2015). IL-12 promotes myeloid-derived suppressor cell recruitment and bacterial persistence during Staphylococcus aureus orthopedic implant infection. J. Immunol. 194, 3861–3872. doi: 10.4049/jimmunol.1402689
Hell, E., Giske, C. G., Nelson, A., Romling, U., and Marchini, G. (2010). Human cathelicidin peptide LL37 inhibits both attachment capability and biofilm formation of Staphylococcus epidermidis. Lett. Appl. Microbiol. 50, 211–215. doi: 10.1111/j.1472-765X.2009.02778.x
Hellmark, B., Unemo, M., Nilsdotter-Augustinsson, A., and Soderquist, B. (2009). Antibiotic susceptibility among Staphylococcus epidermidis isolated from prosthetic joint infections with special focus on rifampicin and variability of the rpoB gene. Clin. Microbiol. Infect. 15, 238–244. doi: 10.1111/j.1469-0691.2008.02663.x
Hirschhausen, N., Schlesier, T., Schmidt, M. A., Gotz, F., Peters, G., and Heilmann, C. (2010). A novel staphylococcal internalization mechanism involves the major autolysin Atl and heat shock cognate protein Hsc70 as host cell receptor. Cell. Microbiol. 12, 1746–1764. doi: 10.1111/j.1462-5822.2010.01506.x
Hogan, S., Stevens, N. T., Humphreys, H., O'Gara, J. P., and O'Neill, E. (2015). Current and future approaches to the prevention and treatment of staphylococcal medical device-related infections. Curr. Pharm. Des. 21, 100–113. doi: 10.2174/1381612820666140905123900
Holland, L. M., Conlon, B., and O'Gara, J. P. (2011). Mutation of tagO reveals an essential role for wall teichoic acids in Staphylococcus epidermidis biofilm development. Microbiology 157(Pt 2), 408–418. doi: 10.1099/mic.0.042234-0
Huang, L. C., Jean, D., Proske, R. J., Reins, R. Y., and McDermott, A. M. (2007). Ocular surface expression and in vitro activity of antimicrobial peptides. Curr. Eye Res. 32, 595–609. doi: 10.1080/02713680701446653
Hussain, M., Heilmann, C., Peters, G., and Herrmann, M. (2001). Teichoic acid enhances adhesion of Staphylococcus epidermidis to immobilized fibronectin. Microb. Pathog. 31, 261–270. doi: 10.1006/mpat.2001.0469
Isiklar, Z. U., Darouiche, R. O., Landon, G. C., and Beck, T. (1996). Efficacy of antibiotics alone for orthopaedic device related infections. Clin. Orthop. Relat. Res. 184–189. doi: 10.1097/00003086-199611000-00025
Iwase, T., Uehara, Y., Shinji, H., Tajima, A., Seo, H., Takada, K., et al. (2010). Staphylococcus epidermidis Esp inhibits Staphylococcus aureus biofilm formation and nasal colonization. Nature 465, 346–349. doi: 10.1038/nature09074
Izano, E. A., Amarante, M. A., Kher, W. B., and Kaplan, J. B. (2008). Differential roles of poly-N-acetylglucosamine surface polysaccharide and extracellular DNA in Staphylococcus aureus and Staphylococcus epidermidis biofilms. Appl. Environ. Microbiol. 74, 470–476. doi: 10.1128/AEM.02073-07
Janek, D., Zipperer, A., Kulik, A., Krismer, B., and Peschel, A. (2016). High frequency and diversity of antimicrobial activities produced by nasal staphylococcus strains against bacterial competitors. PLoS Pathog. 12:e1005812. doi: 10.1371/journal.ppat.1005812
Jensen, L. K., Jensen, H. E., Koch, J., Bjarnsholt, T., Eickhardt, S., and Shirtliff, M. (2015). Specific antibodies to Staphylococcus aureus biofilm are present in serum from pigs with osteomyelitis. In vivo 29, 555–560.
Jilka, R. L., Weinstein, R. S., Bellido, T., Parfitt, A. M., and Manolagas, S. C. (1998). Osteoblast programmed cell death (apoptosis): modulation by growth factors and cytokines. J. Bone Miner. Res. 13, 793–802. doi: 10.1359/jbmr.19220.127.116.113
Jimenez, E., Marin, M. L., Martin, R., Odriozola, J. M., Olivares, M., Xaus, J., et al. (2008). Is meconium from healthy newborns actually sterile? Res. Microbiol. 159, 187–193. doi: 10.1016/j.resmic.2007.12.007
Johns, B. E., Purdy, K. J., Tucker, N. P., and Maddocks, S. E. (2015). Phenotypic and genotypic characteristics of small colony variants and their role in chronic infection. Microbiol. Insights 8, 15–23. doi: 10.4137/MBI.S25800
Kahl, B. C., Becker, K., and Loffler, B. (2016). Clinical significance and pathogenesis of staphylococcal small colony variants in persistent infections. Clin. Microbiol. Rev. 29, 401–427. doi: 10.1128/CMR.00069-15
Khalil, H., Williams, R. J., Stenbeck, G., Henderson, B., Meghji, S., and Nair, S. P. (2007). Invasion of bone cells by Staphylococcus epidermidis. Microb. Infect. 9, 460–465. doi: 10.1016/j.micinf.2007.01.002
Kim, J., Yang, J., Park, O. J., Kang, S. S., Kim, W. S., Kurokawa, K., et al. (2013). Lipoproteins are an important bacterial component responsible for bone destruction through the induction of osteoclast differentiation and activation. J. Bone Miner. Res. 28, 2381–2391. doi: 10.1002/jbmr.1973
Kishimoto, T., Kaneko, T., Ukai, T., Yokoyama, M., Ayon Haro, R., Yoshinaga, Y., et al. (2012). Peptidoglycan and lipopolysaccharide synergistically enhance bone resorption and osteoclastogenesis. J. Periodont. Res. 47, 446–454. doi: 10.1111/j.1600-0765.2011.01452.x
Knobloch, J. K.-M., Jager, S., Horstkotte, M. A., Rohde, H., and Mack, D. (2004). RsbU-dependent regulation of Staphylococcus epidermidis biofilm formation is mediated via the alternative sigma factor sigmaB by repression of the negative regulator gene icaR. Infect. Immun. 72, 3838–3848. doi: 10.1128/IAI.72.7.3838-3848.2004
Kobayashi, K., Takahashi, N., Jimi, E., Udagawa, N., Takami, M., Kotake, S., et al. (2000). Tumor necrosis factor alpha stimulates osteoclast differentiation by a mechanism independent of the ODF/RANKL-RANK interaction. J. Exp. Med. 191, 275–286. doi: 10.1084/jem.191.2.275
Kocianova, S., Vuong, C., Yao, Y., Voyich, J. M., Fischer, E. R., Deleo, F. R., et al. (2005). Key role of poly-gamma-DL-glutamic acid in immune evasion and virulence of Staphylococcus epidermidis. J. Clin. Invest 115, 688–694. doi: 10.1172/JCI200523523
Kretschmer, D., Nikola, N., Durr, M., Otto, M., and Peschel, A. (2012). The virulence regulator Agr controls the staphylococcal capacity to activate human neutrophils via the formyl peptide receptor 2. J. Innate Immun. 4, 201–212. doi: 10.1159/000332142
Kretschmer, D., Rautenberg, M., Linke, D., and Peschel, A. (2015). Peptide length and folding state govern the capacity of staphylococcal beta-type phenol-soluble modulins to activate human formyl-peptide receptors 1 or 2. J. Leukoc. Biol. 97, 689–697. doi: 10.1189/jlb.2A0514-275R
Kristian, S. A., Birkenstock, T. A., Sauder, U., Mack, D., Gotz, F., and Landmann, R. (2008). Biofilm formation induces C3a release and protects Staphylococcus epidermidis from IgG and complement deposition and from neutrophil-dependent killing. J. Infect. Dis. 197, 1028–1035. doi: 10.1086/528992
Kronforst, K. D., Mancuso, C. J., Pettengill, M., Ninkovic, J., Power Coombs, M. R., Stevens, C., et al. (2012). A neonatal model of intravenous Staphylococcus epidermidis infection in mice < 24 h old enables characterization of early innate immune responses. PLoS ONE 7:e43897. doi: 10.1371/journal.pone.0043897
Laborel-Preneron, E., Bianchi, P., Boralevi, F., Lehours, P., Fraysse, F., Morice-Picard, F., et al. (2015). Effects of the Staphylococcus aureus and Staphylococcus epidermidis secretomes isolated from the skin microbiota of atopic children on CD4+ T cell activation. PLoS ONE 10:e0141067. doi: 10.1371/journal.pone.0141067
Lai, Y., Cogen, A. L., Radek, K. A., Park, H. J., Macleod, D. T., Leichtle, A., et al. (2010). Activation of TLR2 by a small molecule produced by Staphylococcus epidermidis increases antimicrobial defense against bacterial skin infections. J. Invest. Dermatol. 130, 2211–2221. doi: 10.1038/jid.2010.123
Lai, Y., Di Nardo, A., Nakatsuji, T., Leichtle, A., Yang, Y., Cogen, A. L., et al. (2009). Commensal bacteria regulate Toll-like receptor 3-dependent inflammation after skin injury. Nat. Med. 15, 1377–1382. doi: 10.1038/nm.2062
Lai, Y., Villaruz, A. E., Li, M., Cha, D. J., Sturdevant, D. E., and Otto, M. (2007). The human anionic antimicrobial peptide dermcidin induces proteolytic defence mechanisms in staphylococci. Mol. Microbiol. 63, 497–506. doi: 10.1111/j.1365-2958.2006.05540.x
Lam, J., Takeshita, S., Barker, J. E., Kanagawa, O., Ross, F. P., and Teitelbaum, S. L. (2000). TNF-alpha induces osteoclastogenesis by direct stimulation of macrophages exposed to permissive levels of RANK ligand. J. Clin. Invest. 106, 1481–1488. doi: 10.1172/JCI11176
Lambe, D. W. Jr., Ferguson, K. P., Mayberry-Carson, K. J., Tober-Meyer, B., and Costerton, J. W. (1991). Foreign-body-associated experimental osteomyelitis induced with Bacteroides fragilis and Staphylococcus epidermidis in rabbits. Clin. Orthop. Relat. Res. 285–294. doi: 10.1097/00003086-199105000-00040
Lankinen, P., Lehtimaki, K., Hakanen, A. J., Roivainen, A., and Aro, H. T. (2012). A comparative 18F-FDG PET/CT imaging of experimental Staphylococcus aureus osteomyelitis and Staphylococcus epidermidis foreign-body-associated infection in the rabbit tibia. EJNMMI Res. 2:41. doi: 10.1186/2191-219X-2-41
Laure, B., Besnier, J. M., Bergemer-Fouquet, A. M., Marquet-Van Der Mee, N., Damie, F., Quentin, R., et al. (2008). Effect of hydroxyapatite coating and polymethylmethacrylate on stainless steel implant-site infection with Staphylococcus epidermidis in a sheep model. J. Biomed. Mater. Res. A 84, 92–98. doi: 10.1002/jbm.a.31376
Lee, J. H., Wang, H., Kaplan, J. B., and Lee, W. Y. (2010). Effects of Staphylococcus epidermidis on osteoblast cell adhesion and viability on a Ti alloy surface in a microfluidic co-culture environment. Acta Biomater. 6, 4422–4429. doi: 10.1016/j.actbio.2010.05.021
Li, D., Lei, H., Li, Z., Li, H., Wang, Y., and Lai, Y. (2013). A novel lipopeptide from skin commensal activates TLR2/CD36-p38 MAPK signaling to increase antibacterial defense against bacterial infection. PLoS ONE 8:e58288. doi: 10.1371/journal.pone.0058288
Li, M., Lai, Y., Villaruz, A. E., Cha, D. J., Sturdevant, D. E., and Otto, M. (2007). Gram-positive three-component antimicrobial peptide-sensing system. Proc. Natl. Acad. Sci. U.S.A. 104, 9469–9474. doi: 10.1073/pnas.0702159104
Los, R., Sawicki, R., Juda, M., Stankevic, M., Rybojad, P., Sawicki, M., et al. (2010). A comparative analysis of phenotypic and genotypic methods for the determination of the biofilm-forming abilities of Staphylococcus epidermidis. FEMS Microbiol. Lett. 310, 97–103. doi: 10.1111/j.1574-6968.2010.02050.x
Lovati, A. B., Drago, L., Bottagisio, M., Bongio, M., Ferrario, M., Perego, S., et al. (2016a). Systemic and local administration of antimicrobial and cell therapies to prevent methicillin-resistant Staphylococcus epidermidis-induced femoral nonunions in a rat model. Mediators Inflamm. 2016:9595706. doi: 10.1155/2016/9595706
Lovati, A. B., Romano, C. L., Bottagisio, M., Monti, L., De Vecchi, E., Previdi, S., et al. (2016b). Modeling staphylococcus epidermidis-induced non-unions: subclinical and clinical evidence in rats. PLoS ONE 11:e0147447. doi: 10.1371/journal.pone.0147447
Mack, D., Davies, A. P., Harris, L. G., Rohde, H., Horstkotte, M. A., and Knobloch, J. K. (2007). Microbial interactions in Staphylococcus epidermidis biofilms. Anal. Bioanal. Chem. 387, 399–408. doi: 10.1007/s00216-006-0745-2
Mack, D., Fischer, W., Krokotsch, A., Leopold, K., Hartmann, R., Egge, H., et al. (1996a). The intercellular adhesin involved in biofilm accumulation of Staphylococcus epidermidis is a linear beta-1,6-linked glucosaminoglycan: purification and structural analysis. J. Bacteriol. 178, 175–183. doi: 10.1128/jb.178.1.175-183.1996
Mack, D., Haeder, M., Siemssen, N., and Laufs, R. (1996b). Association of biofilm production of coagulase-negative staphylococci with expression of a specific polysaccharide intercellular adhesin. J. Infect. Dis. 174, 881–884. doi: 10.1093/infdis/174.4.881
Magrys, A., Paluch-Oles, J., Bogut, A., Kielbus, M., Plewik, D., and Koziol-Montewka, M. (2015). The role of programmed death ligand 1 pathway in persistent biomaterial-associated infections. J. Microbiol. 53, 544–552. doi: 10.1007/s12275-015-5022-7
Majchrzak, K., Mierzwinska-Nastalska, E., Chmura, A., Kwiatkowski, A., Paczek, L., Mlynarczyk, G., et al. (2016). Comparison of staphylococcal flora in denture plaque and the surface of the pharyngeal mucous membrane in kidney transplant recipients. Transplant. Proc. 48, 1590–1597. doi: 10.1016/j.transproceed.2016.03.016
Marmor, S., Bauer, T., Desplaces, N., Heym, B., Roux, A. L., Sol, O., et al. (2016). Multiplex antibody detection for noninvasive genus-level diagnosis of prosthetic joint infection. J. Clin. Microbiol. 54, 1065–1073. doi: 10.1128/JCM.02885-15
Mayberry-Carson, K. J., Tober-Meyer, B., Gill, L. R., Lambe, D. W. Jr., and Hossler, F. E. (1990). Effect of ciprofloxacin on experimental osteomyelitis in the rabbit tibia, induced with a mixed infection of Staphylococcus epidermidis and Bacteroides thetaiotaomicron. Microbios 64, 49–66.
Mayberry-Carson, K. J., Tober-Meyer, B., Lambe, D. W. Jr., and Costerton, J. W. (1992). Osteomyelitis experimentally induced with Bacteroides thetaiotaomicron and Staphylococcus epidermidis. Influence of a foreign-body implant. Clin. Orthop. Relat Res. 280, 289–299. doi: 10.1097/00003086-199207000-00040
Meghji, S., Crean, S. J., Nair, S., Wilson, M., Poole, S., Harris, M., et al. (1997). Staphylococcus epidermidis produces a cell-associated proteinaceous fraction which causes bone resorption by a prostanoid-independent mechanism: relevance to the treatment of infected orthopaedic implants. Br. J. Rheumatol. 36, 957–963. doi: 10.1093/rheumatology/36.9.957
Mehlin, C., Headley, C. M., and Klebanoff, S. J. (1999). An inflammatory polypeptide complex from Staphylococcus epidermidis: isolation and characterization. J. Exp. Med. 189, 907–918. doi: 10.1084/jem.189.6.907
Melzer, M., Eykyn, S. J., Gransden, W. R., and Chinn, S. (2003). Is methicillin-resistant Staphylococcus aureus more virulent than methicillin-susceptible S. aureus? A comparative cohort study of British patients with nosocomial infection and bacteremia. Clin. Infect. Dis. 37, 1453–1460. doi: 10.1086/379321
Mempel, M., Schnopp, C., Hojka, M., Fesq, H., Weidinger, S., Schaller, M., et al. (2002). Invasion of human keratinocytes by Staphylococcus aureus and intracellular bacterial persistence represent haemolysin-independent virulence mechanisms that are followed by features of necrotic and apoptotic keratinocyte cell death. Br. J. Dermatol. 146, 943–951. doi: 10.1046/j.1365-2133.2002.04752.x
Metsemakers, W. J., Kuehl, R., Moriarty, T. F., Richards, R. G., Verhofstad, M. H., Borens, O., et al. (2016). Infection after fracture fixation: current surgical and microbiological concepts. Injury. doi: 10.1016/j.injury.2016.09.019. [Epub ahead of print].
Meyle, E., Brenner-Weiss, G., Obst, U., Prior, B., and Hansch, G. M. (2012). Immune defense against S. epidermidis biofilms: components of the extracellular polymeric substance activate distinct bactericidal mechanisms of phagocytic cells. Int. J. Artif. Organs 35, 700–712. doi: 10.5301/ijao.5000151
Montanaro, L., Speziale, P., Campoccia, D., Ravaioli, S., Cangini, I., Pietrocola, G., et al. (2011). Scenery of Staphylococcus implant infections in orthopedics. Future Microbiol. 6, 1329–1349. doi: 10.2217/fmb.11.117
Morath, S., Stadelmaier, A., Geyer, A., Schmidt, R. R., and Hartung, T. (2002). Synthetic lipoteichoic acid from Staphylococcus aureus is a potent stimulus of cytokine release. J. Exp. Med. 195, 1635–1640. doi: 10.1084/jem.20020322
Morgenstern, M., Erichsen, C., Hackl, S., Mily, J., Militz, M., Friederichs, J., et al. (2016a). Antibiotic resistance of commensal staphylococcus aureus and coagulase-negative staphylococci in an international cohort of surgeons: a prospective point-prevalence study. PLoS ONE 11:e0148437. doi: 10.1371/journal.pone.0148437
Morgenstern, M., Erichsen, C., von Ruden, C., Metsemakers, W. J., Kates, S. L., Moriarty, T. F., et al. (2016b). Staphylococcal orthopaedic device-related infections in older patients. Injury 47, 1427–1434. doi: 10.1016/j.injury.2016.04.027
Morgenstern, M., Post, V., Erichsen, C., Hungerer, S., Buhren, V., Militz, M., et al. (2016c). Biofilm formation increases treatment failure in Staphylococcus epidermidis device-related osteomyelitis of the lower extremity in human patients. J. Orthop. Res. 34, 1905–1913. doi: 10.1002/jor.23218
Moriarty, T. F., Kuehl, R., Coenye, T., Metsemakers, W. J., Morgenstern, M., Schwarz, E. M., et al. (2016). Orthopaedic device-related infection: current and future interventions for improved prevention and treatment. EFORT Open Rev. 1, 89–99. doi: 10.1302/2058-5241.1.000037
Moriarty, T. F., Poulsson, A. H. C., Rochford, E. T. J., and Richards, R. G. (2011). “4.407 - bacterial adhesion and biomaterial surfaces A2” in Comprehensive Biomaterials, ed P. Ducheyne (Oxford: Elsevier), 75–100.
Myrvik, Q. N., Wagner, W., Barth, E., Wood, P., and Gristina, A. G. (1989). Effects of extracellular slime produced by Staphylococcus epidermidis on oxidative responses of rabbit alveolar macrophages. J. Invest. Surg. 2, 381–389. doi: 10.3109/08941938909018263
Naik, S., Bouladoux, N., Linehan, J. L., Han, S. J., Harrison, O. J., Wilhelm, C., et al. (2015). Commensal-dendritic-cell interaction specifies a unique protective skin immune signature. Nature 520, 104–108. doi: 10.1038/nature14052
Nair, N., Vinod, V., Suresh, M. K., Vijayrajratnam, S., Biswas, L., Peethambaran, R., et al. (2015). Amidase, a cell wall hydrolase, elicits protective immunity against Staphylococcus aureus and S. epidermidis. Int. J. Biol. Macromol. 77, 314–321. doi: 10.1016/j.ijbiomac.2015.03.047
Natsuka, M., Uehara, A., Yang, S., Echigo, S., and Takada, H. (2008). A polymer-type water-soluble peptidoglycan exhibited both Toll-like receptor 2- and NOD2-agonistic activities, resulting in synergistic activation of human monocytic cells. Innate Immun. 14, 298–308. doi: 10.1177/1753425908096518
N'Diaye, A. R., Leclerc, C., Kentache, T., Hardouin, J., Poc, C. D., Konto-Ghiorghi, Y., et al. (2016). Skin-bacteria communication: involvement of the neurohormone Calcitonin Gene Related Peptide (CGRP) in the regulation of Staphylococcus epidermidis virulence. Sci. Rep. 6:35379. doi: 10.1038/srep35379
Nilsdotter-Augustinsson, A., Wilsson, A., Larsson, J., Stendahl, O., Ohman, L., and Lundqvist-Gustafsson, H. (2004). Staphylococcus aureus, but not Staphylococcus epidermidis, modulates the oxidative response and induces apoptosis in human neutrophils. APMIS 112, 109–118. doi: 10.1111/j.1600-0463.2004.apm1120205.x
Ommori, R., Ouji, N., Mizuno, F., Kita, E., Ikada, Y., and Asada, H. (2013). Selective induction of antimicrobial peptides from keratinocytes by staphylococcal bacteria. Microb. Pathog. 56, 35–39. doi: 10.1016/j.micpath.2012.11.005
Osmon, D. R., Berbari, E. F., Berendt, A. R., Lew, D., Zimmerli, W., Steckelberg, J. M., et al. (2013). Diagnosis and management of prosthetic joint infection: clinical practice guidelines by the Infectious Diseases Society of America. Clin. Infect. Dis. 56, e1–e25. doi: 10.1093/cid/cis966
Park, B., Iwase, T., and Liu, G. Y. (2011). Intranasal application of S. epidermidis prevents colonization by methicillin-resistant Staphylococcus aureus in mice. PLoS ONE 6:e25880. doi: 10.1371/journal.pone.0025880
Park, K. H., Greenwood-Quaintance, K. E., Schuetz, A. N., Mandrekar, J. N., and Patel, R. (2016). Activity of tedizolid in methicillin-resistant Staphylococcus aureus experimental foreign body-associated osteomyelitis. Antimicrob. Agents Chemother. 60, 6568–6572. doi: 10.1128/AAC.01248-16
Park, K., Ommori, R., Imoto, K., and Asada, H. (2014). Epidermal growth factor receptor inhibitors selectively inhibit the expressions of human beta-defensins induced by Staphylococcus epidermidis. J. Dermatol. Sci. 75, 94–99. doi: 10.1016/j.jdermsci.2014.04.011
Patel, M., and Kaufman, D. A. (2015). Anti-lipoteichoic acid monoclonal antibody (pagibaximab) studies for the prevention of staphylococcal bloodstream infections in preterm infants. Expert Opin. Biol. Ther. 15, 595–600. doi: 10.1517/14712598.2015.1019857
Patzakis, M. J., and Zalavras, C. G. (2005). Chronic posttraumatic osteomyelitis and infected nonunion of the tibia: current management concepts. J. Am. Acad. Orthop. Surg. 13, 417–427. doi: 10.5435/00124635-200510000-00006
Percoco, G., Merle, C., Jaouen, T., Ramdani, Y., Benard, M., Hillion, M., et al. (2013). Antimicrobial peptides and pro-inflammatory cytokines are differentially regulated across epidermal layers following bacterial stimuli. Exp. Dermatol. 22, 800–806. doi: 10.1111/exd.12259
Perks, W. V., Singh, R. K., Jones, G. W., Twohig, J. P., Williams, A. S., Humphreys, I. R., et al. (2016). Death receptor 3 promotes chemokine-directed leukocyte recruitment in acute resolving inflammation and is essential for pathological development of mesothelial fibrosis in chronic disease. Am. J. Pathol. 186, 2813–2823. doi: 10.1016/j.ajpath.2016.07.021
Peschel, A., Otto, M., Jack, R. W., Kalbacher, H., Jung, G., and Gotz, F. (1999). Inactivation of the dlt operon in Staphylococcus aureus confers sensitivity to defensins, protegrins, and other antimicrobial peptides. J. Biol. Chem. 274, 8405–8410. doi: 10.1074/jbc.274.13.8405
Petty, W., Spanier, S., Shuster, J. J., and Silverthorne, C. (1985). The influence of skeletal implants on incidence of infection. Experiments in a canine model. J. Bone Joint Surg. Am. 67, 1236–1244. doi: 10.2106/00004623-198567080-00015
Pietrocola, G., Arciola, C. R., Rindi, S., Di Poto, A., Missineo, A., Montanaro, L., et al. (2011). Toll-like receptors (TLRs) in innate immune defense against Staphylococcus aureus. Int. J. Artif. Organs 34, 799–810. doi: 10.5301/ijao.5000030
Pinheiro, L., Brito, C. I., Pereira, V. C., Oliveira, A., Bartolomeu, A. R., Camargo, C. H., et al. (2016). Susceptibility profile of Staphylococcus epidermidis and staphylococcus haemolyticus isolated from blood cultures to vancomycin and novel antimicrobial drugs over a period of 12 years. Microb. Drug Resist. 22, 283–293. doi: 10.1089/mdr.2015.0064
Pourmand, M. R., Clarke, S. R., Schuman, R. F., Mond, J. J., and Foster, S. J. (2006). Identification of antigenic components of Staphylococcus epidermidis expressed during human infection. Infect. Immun. 74, 4644–4654. doi: 10.1128/IAI.00521-06
Prabhakara, R., Harro, J. M., Leid, J. G., Harris, M., and Shirtliff, M. E. (2011a). Murine immune response to a chronic Staphylococcus aureus biofilm infection. Infect. Immun. 79, 1789–1796. doi: 10.1128/IAI.01386-10
Prabhakara, R., Harro, J. M., Leid, J. G., Keegan, A. D., Prior, M. L., and Shirtliff, M. E. (2011b). Suppression of the inflammatory immune response prevents the development of chronic biofilm infection due to methicillin-resistant Staphylococcus aureus. Infect. Immun. 79, 5010–5018. doi: 10.1128/IAI.05571-11
Puig-Verdie, L., Alentorn-Geli, E., Gonzalez-Cuevas, A., Sorli, L., Salvado, M., Alier, A., et al. (2013). Implant sonication increases the diagnostic accuracy of infection in patients with delayed, but not early, orthopaedic implant failure. Bone Joint J. 95B, 244–249. doi: 10.1302/0301-620X.95B2.30486
Qin, L., Da, F., Fisher, E. L., Tan, D. C., Nguyen, T. H., Fu, C. L., et al. (2017). Toxin mediates sepsis caused by methicillin-resistant Staphylococcus epidermidis. PLoS Pathog. 13:e1006153. doi: 10.1371/journal.ppat.1006153
Qin, L., McCausland, J. W., Cheung, G. Y., and Otto, M. (2016). PSM-Mec-a virulence determinant that connects transcriptional regulation, virulence, and antibiotic resistance in staphylococci. Front. Microbiol. 7:1293. doi: 10.3389/fmicb.2016.01293
Qin, Z., Ou, Y., Yang, L., Zhu, Y., Tolker-Nielsen, T., Molin, S., et al. (2007). Role of autolysin-mediated DNA release in biofilm formation of Staphylococcus epidermidis. Microbiology 153, 2083–2092. doi: 10.1099/mic.0.2007/006031-0
Quinn, J. M., Athanasou, N. A., and McGee, J. O. (1991). Extracellular matrix receptor and platelet antigens on osteoclasts and foreign body giant cells. Histochemistry 96, 169–176. doi: 10.1007/BF00315989
Rautenberg, M., Joo, H. S., Otto, M., and Peschel, A. (2011). Neutrophil responses to staphylococcal pathogens and commensals via the formyl peptide receptor 2 relates to phenol-soluble modulin release and virulence. FASEB J. 25, 1254–1263. doi: 10.1096/fj.10-175208
Riool, M., de Boer, L., Jaspers, V., van der Loos, C. M., van Wamel, W. J., Wu, G., et al. (2014). Staphylococcus epidermidis originating from titanium implants infects surrounding tissue and immune cells. Acta Biomater. 10, 5202–5212. doi: 10.1016/j.actbio.2014.08.012
Robertson, J., Lang, S., Lambert, P. A., and Martin, P. E. (2010). Peptidoglycan derived from Staphylococcus epidermidis induces Connexin43 hemichannel activity with consequences on the innate immune response in endothelial cells. Biochem. J. 432, 133–143. doi: 10.1042/BJ20091753
Rochford, E. T., Sabate Bresco, M., Zeiter, S., Kluge, K., Poulsson, A., Ziegler, M., et al. (2016). Monitoring immune responses in a mouse model of fracture fixation with and without Staphylococcus aureus osteomyelitis. Bone 83, 82–92. doi: 10.1016/j.bone.2015.10.014
Rohde, H., Burandt, E. C., Siemssen, N., Frommelt, L., Burdelski, C., Wurster, S., et al. (2007). Polysaccharide intercellular adhesin or protein factors in biofilm accumulation of Staphylococcus epidermidis and Staphylococcus aureus isolated from prosthetic hip and knee joint infections. Biomaterials 28, 1711–1720. doi: 10.1016/j.biomaterials.2006.11.046
Rohde, H., Burdelski, C., Bartscht, K., Hussain, M., Buck, F., Horstkotte, M. A., et al. (2005). Induction of Staphylococcus epidermidis biofilm formation via proteolytic processing of the accumulation-associated protein by staphylococcal and host proteases. Mol. Microbiol. 55, 1883–1895. doi: 10.1111/j.1365-2958.2005.04515.x
Rohde, H., Kalitzky, M., Kroger, N., Scherpe, S., Horstkotte, M. A., Knobloch, J. K., et al. (2004). Detection of virulence-associated genes not useful for discriminating between invasive and commensal Staphylococcus epidermidis strains from a bone marrow transplant unit. J. Clin. Microbiol. 42, 5614–5619. doi: 10.1128/JCM.42.12.5614-5619.2004
Rolo, J., de Lencastre, H., and Miragaia, M. (2012). Strategies of adaptation of Staphylococcus epidermidis to hospital and community: amplification and diversification of SCCmec. J. Antimicrob. Chemother. 67, 1333–1341. doi: 10.1093/jac/dks068
Sadovskaya, I., Faure, S., Watier, D., Leterme, D., Chokr, A., Girard, J., et al. (2007). Potential use of poly-N-acetyl-beta-(1,6)-glucosamine as an antigen for diagnosis of staphylococcal orthopedic-prosthesis-related infections. Clin. Vaccine Immunol. 14, 1609–1615. doi: 10.1128/CVI.00215-07
Salgado, C. D., Dash, S., Cantey, J. R., and Marculescu, C. E. (2007). Higher risk of failure of methicillin-resistant Staphylococcus aureus prosthetic joint infections. Clin. Orthop. Relat. Res. 461, 48–53. doi: 10.1097/blo.0b013e3181123d4e
Salgueiro, V. C., Iorio, N. L., Ferreira, M. C., Chamon, R. C., and Dos Santos, K. R. (2017). Methicillin resistance and virulence genes in invasive and nasal Staphylococcus epidermidis isolates from neonates. BMC Microbiol. 17:15. doi: 10.1186/s12866-017-0930-9
Sandiford, S., and Upton, M. (2012). Identification, characterization, and recombinant expression of epidermicin NI01, a novel unmodified bacteriocin produced by Staphylococcus epidermidis that displays potent activity against Staphylococci. Antimicrob. Agents Chemother. 56, 1539–1547. doi: 10.1128/AAC.05397-11
Satorius, A. E., Szafranski, J., Pyne, D., Ganesan, M., Solomon, M. J., Newton, D. W., et al. (2013). Complement c5a generation by staphylococcal biofilms. Shock 39, 336–342. doi: 10.1097/SHK.0b013e31828d9324
Schafer, P., Fink, B., Sandow, D., Margull, A., Berger, I., and Frommelt, L. (2008). Prolonged bacterial culture to identify late periprosthetic joint infection: a promising strategy. Clin. Infect. Dis. 47, 1403–1409. doi: 10.1086/592973
Scharschmidt, T. C., Vasquez, K. S., Truong, H. A., Gearty, S. V., Pauli, M. L., Nosbaum, A., et al. (2015). A wave of regulatory T cells into neonatal skin mediates tolerance to commensal microbes. Immunity 43, 1011–1021. doi: 10.1016/j.immuni.2015.10.016
Scherr, T. D., Lindgren, K. E., Schaeffer, C. R., Hanke, M. L., Hartman, C. W., and Kielian, T. (2014). Mouse model of post-arthroplasty Staphylococcus epidermidis joint infection. Methods Mol. Biol. 1106, 173–181. doi: 10.1007/978-1-62703-736-5_16
Schommer, N. N., Christner, M., Hentschke, M., Ruckdeschel, K., Aepfelbacher, M., and Rohde, H. (2011). Staphylococcus epidermidis uses distinct mechanisms of biofilm formation to interfere with phagocytosis and activation of mouse macrophage-like cells 774A.1. Infect. Immun. 79, 2267–2276. doi: 10.1128/IAI.01142-10
Sellman, B. R., Howell, A. P., Kelly-Boyd, C., and Baker, S. M. (2005). Identification of immunogenic and serum binding proteins of Staphylococcus epidermidis. Infect. Immun. 73, 6591–6600. doi: 10.1128/IAI.73.10.6591-6600.2005
Shahrooei, M., Hira, V., Khodaparast, L., Khodaparast, L., Stijlemans, B., Kucharikova, S., et al. (2012). Vaccination with SesC decreases Staphylococcus epidermidis biofilm formation. Infect. Immun. 80, 3660–3668. doi: 10.1128/IAI.00104-12
Shahrooei, M., Hira, V., Stijlemans, B., Merckx, R., Hermans, P. W. M., and Van Eldere, J. (2009). Inhibition of Staphylococcus epidermidis Biofilm Formation by Rabbit Polyclonal Antibodies against the SesC Protein. Infect. Immun. 77, 3670–3678. doi: 10.1128/IAI.01464-08
Sharon, I., Morowitz, M. J., Thomas, B. C., Costello, E. K., Relman, D. A., and Banfield, J. F. (2013). Time series community genomics analysis reveals rapid shifts in bacterial species, strains, and phage during infant gut colonization. Genome Res. 23, 111–120. doi: 10.1101/gr.142315.112
Shurland, S., Zhan, M., Bradham, D. D., and Roghmann, M. C. (2007). Comparison of mortality risk associated with bacteremia due to methicillin-resistant and methicillin-susceptible Staphylococcus aureus. Infect. Control Hosp. Epidemiol. 28, 273–279. doi: 10.1086/512627
Simojoki, H., Salomaki, T., Taponen, S., Iivanainen, A., and Pyorala, S. (2011). Innate immune response in experimentally induced bovine intramammary infection with Staphylococcus simulans and S. epidermidis. Vet. Res. 42:49. doi: 10.1186/1297-9716-42-49
Sinha, B., Francois, P. P., Nusse, O., Foti, M., Hartford, O. M., Vaudaux, P., et al. (1999). Fibronectin-binding protein acts as Staphylococcus aureus invasin via fibronectin bridging to integrin alpha5beta1. Cell. Microbiol. 1, 101–117. doi: 10.1046/j.1462-5822.1999.00011.x
Somayaji, S. N., Ritchie, S., Sahraei, M., Marriott, I., and Hudson, M. C. (2008). Staphylococcus aureus induces expression of receptor activator of NF-kappaB ligand and prostaglandin E2 in infected murine osteoblasts. Infect. Immun. 76, 5120–5126. doi: 10.1128/IAI.00228-08
Spiliopoulou, A. I., Kolonitsiou, F., Krevvata, M. I., Leontsinidis, M., Wilkinson, T. S., Mack, D., et al. (2012). Bacterial adhesion, intracellular survival and cytokine induction upon stimulation of mononuclear cells with planktonic or biofilm phase Staphylococcus epidermidis. FEMS Microbiol. Lett. 330, 56–65. doi: 10.1111/j.1574-6968.2012.02533.x
Stanislawska, J., Interewicz, B., Maksymowicz, M., Moscicka, M., and Olszewski, W. L. (2005). The response of spleen dendritic cell-enriched population to bacterial and allogeneic antigens. Ann. Transplant. 10, 17–23.
Stashenko, P., Dewhirst, F. E., Rooney, M. L., Desjardins, L. A., and Heeley, J. D. (1987). Interleukin-1 beta is a potent inhibitor of bone formation in vitro. J. Bone Miner. Res. 2, 559–565. doi: 10.1002/jbmr.5650020612
Strunk, T., Power Coombs, M. R., Currie, A. J., Richmond, P., Golenbock, D. T., Stoler-Barak, L., et al. (2010). TLR2 mediates recognition of live Staphylococcus epidermidis and clearance of bacteremia. PLoS ONE 5:e10111. doi: 10.1371/journal.pone.0010111
Strunk, T., Prosser, A., Levy, O., Philbin, V., Simmer, K., Doherty, D., et al. (2012). Responsiveness of human monocytes to the commensal bacterium Staphylococcus epidermidis develops late in gestation. Pediatr. Res. 72, 10–18. doi: 10.1038/pr.2012.48
Sugimoto, S., Iwamoto, T., Takada, K., Okuda, K., Tajima, A., Iwase, T., et al. (2013). Staphylococcus epidermidis Esp degrades specific proteins associated with Staphylococcus aureus biofilm formation and host-pathogen interaction. J. Bacteriol. 195, 1645–1655. doi: 10.1128/JB.01672-12
Sullivan, S. B., Kamath, S., McConville, T. H., Gray, B. T., Lowy, F. D., Gordon, P. G., et al. (2016). Staphylococcus epidermidis protection against staphylococcus aureus colonization in people living with human immunodeficiency virus in an inner-city outpatient population: a cross-sectional study. Open Forum Infect Dis 3:ofw234. doi: 10.1093/ofid/ofw234
Svensson, S., Trobos, M., Hoffman, M., Norlindh, B., Petronis, S., Lausmaa, J., et al. (2015). A novel soft tissue model for biomaterial-associated infection and inflammation - bacteriological, morphological and molecular observations. Biomaterials 41, 106–121. doi: 10.1016/j.biomaterials.2014.11.032
Svensson, S., Trobos, M., Omar, O., and Thomsen, P. (2017). Site-specific gene expression analysis of implant-near cells in a soft tissue infection model - application of laser microdissection to study biomaterial-associated infection. J. Biomed. Mater. Res. A. 105, 2210–2217. doi: 10.1002/jbm.a.36088
Tan, H. L., Ao, H. Y., Ma, R., Lin, W. T., and Tang, T. T. (2014). In vivo effect of quaternized chitosan-loaded polymethylmethacrylate bone cement on methicillin-resistant Staphylococcus epidermidis infection of the tibial metaphysis in a rabbit model. Antimicrob. Agents Chemother. 58, 6016–6023. doi: 10.1128/AAC.03489-14
Tavakkol, Z., Samuelson, D., deLancey Pulcini, E., Underwood, R. A., Usui, M. L., Costerton, J. W., et al. (2010). Resident bacterial flora in the skin of C57BL/6 mice housed under SPF conditions. J. Am. Assoc. Lab. Anim. Sci. 49, 588–591.
Teterycz, D., Ferry, T., Lew, D., Stern, R., Assal, M., Hoffmeyer, P., et al. (2010). Outcome of orthopedic implant infections due to different staphylococci. Int. J. Infect. Dis. 14, e913–918. doi: 10.1016/j.ijid.2010.05.014
Tormo, M. A., Knecht, E., Gotz, F., Lasa, I., and Penades, J. R. (2005). Bap-dependent biofilm formation by pathogenic species of Staphylococcus: evidence of horizontal gene transfer? Microbiology 151(Pt 7), 2465–2475. doi: 10.1099/mic.0.27865-0
Trampuz, A., Piper, K. E., Jacobson, M. J., Hanssen, A. D., Unni, K. K., Osmon, D. R., et al. (2007). Sonication of removed hip and knee prostheses for diagnosis of infection. New Engl. J. Med. 357, 654–663. doi: 10.1056/NEJMoa061588
Trouillet-Assant, S., Gallet, M., Nauroy, P., Rasigade, J. P., Flammier, S., Parroche, P., et al. (2015). Dual impact of live Staphylococcus aureus on the osteoclast lineage, leading to increased bone resorption. J. Infect. Dis. 211, 571–581. doi: 10.1093/infdis/jiu386
Tucker, K. A., Reilly, S. S., Leslie, C. S., and Hudson, M. C. (2000). Intracellular Staphylococcus aureus induces apoptosis in mouse osteoblasts. FEMS Microbiol. Lett. 186, 151–156. doi: 10.1111/j.1574-6968.2000.tb09096.x
Turner, J., Cho, Y., Dinh, N. N., Waring, A. J., and Lehrer, R. I. (1998). Activities of LL-37, a cathelin-associated antimicrobial peptide of human neutrophils. Antimicrob. Agents Chemother. 42, 2206–2214.
Usui, Y., Ohshima, Y., Ichiman, Y., Ohtomo, T., Suganuma, M., and Yoshida, K. (1991). Platelet aggregation induced by strains of various species of coagulase-negative staphylococci. Microbiol. Immunol. 35, 15–26. doi: 10.1111/j.1348-0421.1991.tb01529.x
Valour, F., Trouillet-Assant, S., Rasigade, J. P., Lustig, S., Chanard, E., Meugnier, H., et al. (2013). Staphylococcus epidermidis in orthopedic device infections: the role of bacterial internalization in human osteoblasts and biofilm formation. PLoS ONE 8:e67240. doi: 10.1371/journal.pone.0067240
van Bergenhenegouwen, J., Plantinga, T. S., Joosten, L. A., Netea, M. G., Folkerts, G., Kraneveld, A. D., et al. (2013). TLR2 and Co: a critical analysis of the complex interactions between TLR2 and coreceptors. J. Leukoc. Biol. 94, 885–902. doi: 10.1189/jlb.0113003
van de Kamp, M., Horstink, L. M., van den Hooven, H. W., Konings, R. N., Hilbers, C. W., Frey, A., et al. (1995). Sequence analysis by NMR spectroscopy of the peptide lantibiotic epilancin K7 from Staphylococcus epidermidis K7. Eur. J. Biochem. 227, 757–771. doi: 10.1111/j.1432-1033.1995.tb20199.x
van der Borden, A. J., Maathuis, P. G., Engels, E., Rakhorst, G., van der Mei, H. C., Busscher, H. J., et al. (2007). Prevention of pin tract infection in external stainless steel fixator frames using electric current in a goat model. Biomaterials 28, 2122–2126. doi: 10.1016/j.biomaterials.2007.01.001
Veenstra, G., Cremers, F., van Dijk, H., and Fleer, A. (1996). Ultrastructural organization and regulation of a biomaterial adhesin of Staphylococcus epidermidis. J. Bacteriol. 178, 537–541. doi: 10.1128/jb.178.2.537-541.1996
Vernachio, J. H., Bayer, A. S., Ames, B., Bryant, D., Prater, B. D., Syribeys, P. J., et al. (2006). Human immunoglobulin G recognizing fibrinogen-binding surface proteins is protective against both Staphylococcus aureus and Staphylococcus epidermidis infections in vivo. Antimicrob. Agents Chemother. 50, 511–518. doi: 10.1128/AAC.50.2.511-518.2006
Vuong, C., Durr, M., Carmody, A. B., Peschel, A., Klebanoff, S. J., and Otto, M. (2004a). Regulated expression of pathogen-associated molecular pattern molecules in Staphylococcus epidermidis: quorum-sensing determines pro-inflammatory capacity and production of phenol-soluble modulins. Cell. Microbiol. 6, 753–759. doi: 10.1111/j.1462-5822.2004.00401.x
Vuong, C., Gerke, C., Somerville, G. A., Fischer, E. R., and Otto, M. (2003). Quorum-sensing control of biofilm factors in Staphylococcus epidermidis. J. Infect. Dis. 188, 706–718. doi: 10.1086/377239
Vuong, C., Kocianova, S., Voyich, J. M., Yao, Y., Fischer, E. R., Deleo, F. R., et al. (2004b). A crucial role for exopolysaccharide modification in bacterial biofilm formation, immune evasion, and virulence. J. Biol. Chem. 279, 54881–54886. doi: 10.1074/jbc.M411374200
Vuong, C., Kocianova, S., Yu, J., Kadurugamuwa, J. L., and Otto, M. (2008). Development of real-time in vivo imaging of device-related Staphylococcus epidermidis infection in mice and influence of animal immune status on susceptibility to infection. J. Infect. Dis. 198, 258–261. doi: 10.1086/589307
Vuong, C., Voyich, J. M., Fischer, E. R., Braughton, K. R., Whitney, A. R., Deleo, F. R., et al. (2004c). Polysaccharide intercellular adhesin (PIA) protects Staphylococcus epidermidis against major components of the human innate immune system. Cell. Microbiol. 6, 269–275. doi: 10.1046/j.1462-5822.2004.00367.x
Wakabayashi, G., Gelfand, J. A., Jung, W. K., Connolly, R. J., Burke, J. F., and Dinarello, C. A. (1991). Staphylococcus epidermidis induces complement activation, tumor necrosis factor and interleukin-1, a shock-like state and tissue injury in rabbits without endotoxemia. Comparison to Escherichia coli. J. Clin. Invest. 87, 1925–1935. doi: 10.1172/JCI115218
Wang, R., Khan, B. A., Cheung, G. Y., Bach, T. H., Jameson-Lee, M., Kong, K. F., et al. (2011). Staphylococcus epidermidis surfactant peptides promote biofilm maturation and dissemination of biofilm-associated infection in mice. J. Clin. Invest. 121, 238–248. doi: 10.1172/JCI42520
Wang, Y., Kuo, S., Shu, M., Yu, J., Huang, S., Dai, A., et al. (2014). Staphylococcus epidermidis in the human skin microbiome mediates fermentation to inhibit the growth of Propionibacterium acnes: implications of probiotics in acne vulgaris. Appl. Microbiol. Biotechnol. 98, 411–424. doi: 10.1007/s00253-013-5394-8
Wanke, I., Steffen, H., Christ, C., Krismer, B., Gotz, F., Peschel, A., et al. (2011). Skin commensals amplify the innate immune response to pathogens by activation of distinct signaling pathways. J. Invest. Dermatol. 131, 382–390. doi: 10.1038/jid.2010.328
Webster, T. J., Patel, A. A., Rahaman, M. N., and Sonny Bal, B. (2012). Anti-infective and osteointegration properties of silicon nitride, poly(ether ether ketone), and titanium implants. Acta Biomater. 8, 4447–4454. doi: 10.1016/j.actbio.2012.07.038
Widerstrom, M. (2016). Significance of Staphylococcus epidermidis in health care-associated infections, from contaminant to clinically relevant pathogen: this is a wake-up call! J. Clin. Microbiol. 54, 1679–1681. doi: 10.1128/JCM.00743-16
Widerstrom, M., Wistrom, J., Edebro, H., Marklund, E., Backman, M., Lindqvist, P., et al. (2016). Colonization of patients, healthcare workers, and the environment with healthcare-associated Staphylococcus epidermidis genotypes in an intensive care unit: a prospective observational cohort study. BMC Infect. Dis. 16:743. doi: 10.1186/s12879-016-2094-x
Williams, R. J., Henderson, B., Sharp, L. J., and Nair, S. P. (2002). Identification of a fibronectin-binding protein from Staphylococcus epidermidis. Infect. Immun. 70, 6805–6810. doi: 10.1128/IAI.70.12.6805-6810.2002
Wilsson, A., Lind, S., Ohman, L., Nilsdotter-Augustinsson, A., and Lundqvist-Setterud, H. (2008). Apoptotic neutrophils containing Staphylococcus epidermidis stimulate macrophages to release the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6. FEMS Immunol. Med. Microbiol. 53, 126–135. doi: 10.1111/j.1574-695X.2008.00412.x
Xia, X., Li, Z., Liu, K., Wu, Y., Jiang, D., and Lai, Y. (2016). Staphylococcal LTA-induced miR-143 inhibits propionibacterium acnes-mediated inflammatory response in skin. J. Invest. Dermatol. 136, 621–630. doi: 10.1016/j.jid.2015.12.024
Xu, L., Li, H., Vuong, C., Vadyvaloo, V., Wang, J., Yao, Y., et al. (2006). Role of the luxS quorum-sensing system in biofilm formation and virulence of Staphylococcus epidermidis. Infect. Immun. 74, 488–496. doi: 10.1128/IAI.74.1.488-496.2006
Xu, Y., Larsen, L. H., Lorenzen, J., Hall-Stoodley, L., Kikhney, J., Moter, A., et al. (2017). Microbiological diagnosis of device-related biofilm infections. APMIS 125, 289–303. doi: 10.1111/apm.12676
Yan, L., Zhang, L., Ma, H., Chiu, D., and Bryers, J. D. (2014). A Single B-repeat of Staphylococcus epidermidis accumulation-associated protein induces protective immune responses in an experimental biomaterial-associated infection mouse model. Clin. Vaccine Immunol. 21, 1206–1214. doi: 10.1128/CVI.00306-14
Yang, J., Ryu, Y. H., Yun, C. H., and Han, S. H. (2009). Impaired osteoclastogenesis by staphylococcal lipoteichoic acid through Toll-like receptor 2 with partial involvement of MyD88. J. Leukoc. Biol. 86, 823–831. doi: 10.1189/jlb.0309206
Yano, M. H., Klautau, G. B., da Silva, C. B., Nigro, S., Avanzi, O., Mercadante, M. T., et al. (2014). Improved diagnosis of infection associated with osteosynthesis by use of sonication of fracture fixation implants. J. Clin. Microbiol. 52, 4176–4182. doi: 10.1128/JCM.02140-14
Yao, Y., Sturdevant D. E., and Otto, M. (2005). Genomewide analysis of gene expression in Staphylococcus epidermidis biofilms: insights into the pathophysiology of S. epidermidis biofilms and the role of phenol soluble modulins in formation of biofilms. J. Infect. Dis. 191, 289–298. doi: 10.1086/426945
Yoshimura, A., Lien, E., Ingalls, R. R., Tuomanen, E., Dziarski, R., and Golenbock, D. (1999). Cutting edge: recognition of Gram-positive bacterial cell wall components by the innate immune system occurs via Toll-like receptor 2. J. Immunol. 163, 1–5.
Young, A. B., Cooley, I. D., Chauhan, V. S., and Marriott, I. (2011). Causative agents of osteomyelitis induce death domain-containing TNF-related apoptosis-inducing ligand receptor expression on osteoblasts. Bone 48, 857–863. doi: 10.1016/j.bone.2010.11.015
Zaatreh, S., Wegner, K., Strauss, M., Pasold, J., Mittelmeier, W., Podbielski, A., et al. (2016). Co-Culture of S. epidermidis and human osteoblasts on implant surfaces: an advanced in vitro model for implant-associated infections. PLoS ONE 11:e0151534. doi: 10.1371/journal.pone.0151534
Zhai, H., Pan, J., Pang, E., and Bai, B. (2014). Lavage with allicin in combination with vancomycin inhibits biofilm formation by Staphylococcus epidermidis in a rabbit model of prosthetic joint infection. PLoS ONE 9:e102760. doi: 10.1371/journal.pone.0102760
Zhang, Y.-Q., Ren, S.-X., Li, H.-L., Wang, Y.-X., Fu, G., Yang, J., et al. (2003). Genome-based analysis of virulence genes in a non-biofilm-forming Staphylococcus epidermidis strain (ATCC 12228). Mol. Microbiol. 49, 1577–1593. doi: 10.1046/j.1365-2958.2003.03671.x
Zhu, C., Tan, H., Cheng, T., Shen, H., Shao, J., Guo, Y., et al. (2013). Human beta-defensin 3 inhibits antibiotic-resistant Staphylococcus biofilm formation. J. Surg. Res. 183, 204–213. doi: 10.1016/j.jss.2012.11.048
Keywords: Staphylococcus epidermidis, coagulase-negative staphylococci, commensal bacteria, device-related infection, bone infection, biofilm, immune responses
Citation: Sabaté Brescó M, Harris LG, Thompson K, Stanic B, Morgenstern M, O'Mahony L, Richards RG and Moriarty TF (2017) Pathogenic Mechanisms and Host Interactions in Staphylococcus epidermidis Device-Related Infection. Front. Microbiol. 8:1401. doi: 10.3389/fmicb.2017.01401
Received: 03 May 2017; Accepted: 11 July 2017;
Published: 02 August 2017.
Edited by:Laurel L. Lenz, University of Colorado Denver School of Medicine, United States
Reviewed by:Rebecca Leigh Schmidt, Upper Iowa University, United States
Manuel Vilanova, Universidade do Porto, Portugal
Copyright © 2017 Sabaté Brescó, Harris, Thompson, Stanic, Morgenstern, O'Mahony, Richards and Moriarty. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: T. Fintan Moriarty, email@example.com