Otitis Media Caused by V. cholerae O100: A Case Report and Review of the Literature

Infections due to Vibrio cholerae are rarely documented in Israel. Here we report a case of recurrent otitis media in a young male, caused by V. cholerae non-O1/O139. This extra-intestinal infection was caused by V. cholerae O100 and has been associated with freshwater exposure and travel. Symptoms of chronic periodic earaches along with purulent exudate began about one week after the patient suffered a water skiing accident on a river in Australia. The condition lasted for three years, until his ear exudate was examined in a clinical laboratory, diagnosed and treated. Five bacterial isolates were identified as V. cholerae O100. The isolates were screened for genetic characteristics and were found positive for the presence of hapA, hlyA, and ompU virulence genes. All isolates were negative for the presence of ctxA. Based on antibiogram susceptibility testing, ciprofloxacin ear drops were used until the patient’s symptoms disappeared. This case demonstrates that exposure to freshwater can cause otitis media by V. cholerae non-O1/O139 in young and otherwise healthy humans.


INTRODUCTION
Vibrio cholerae is a Gram-negative comma-shaped, facultative anaerobic, motile bacterium, belonging to the Vibrionaceae family. V. cholerae is both a human pathogen and a natural inhabitant of aquatic environments (Colwell et al., 1977;Cottingham et al., 2003). Infections are primarily associated with ingestion of contaminated foods and water, with subsequent diarrheal illness. This species is divided into more than 200 serogroups, of which only O1 and O139 cause cholera epidemics and pandemics (Harris et al., 2012;Clemens et al., 2017).
Vibrio cholerae is a waterborn bacterium and can be found in marine and freshwaters (Clemens et al., 2017). It has been associated with various reservoirs in the aquatic environment: chitinous organisms, i.e., crustaceans and especially copepods (Vezzulli et al., 2010); chironomids (Broza and Halpern, 2001;Halpern et al., 2004Halpern et al., , 2006Halpern et al., , 2007Senderovich et al., 2008;Halpern and Senderovich, 2015); phytoplankton and aquatic plants (Islam et al., 2006;Seeligmann et al., 2008); protozoa (Barker and Brown, 1994); waterfowl, which may be the disseminators of V. cholerae between water bodies, both within and between continents ; fish, which consume chironomids and copepods, on one hand, and are consumed by waterfowl on the other, carry V. cholerae in their intestine and may play an important role in V. cholerae dissemination (Senderovich et al., 2010;Halpern and Izhaki, 2017). Furthermore, in addition to the particle-associated growth strategy of environmental V. cholerae, few reports have demonstrated that V. cholerae can also grow in water as a free-living organism in the planktonic phase (Worden et al., 2006).
We report here a case of non-O1/O139 V. cholerae otitis media which developed in a young male after a water skiing accident.

Ethics Statement
This study was carried out in accordance with the recommendations of the guidelines of Helsinki Committee and was approved by the Helsinki Committee of Clalit Health Services, Israel (approval no. 0192-15-COM1). The subject gave a written informed consent in accordance with the Declaration of Helsinki.
A 27-years old Caucasian male with acute otitis media presented to an otolaryngologist at a medical clinic in Haifa, Israel, after suffering for a period of three years from a periodic earache accompanied by a malodorous and purulent exudate from his right ear, without fever. As the patient recalled, the onset of the symptoms began approximately one week after his 2011 water skiing accident on the Murray River near Mildura, VIC, Australia, in which he fell and perforated his right eardrum.
Prior to his admission, and with the onset of the periodic ear exudates, the patient had undergone a series of ear cleansings and aspirations without any significant improvement. During his admission, an ear swab was used to sample his exudate, and later was sent to the microbiology laboratory of Clalit Health Services of Haifa and Western Galilee district for further analysis.
Twelve hours after initial incubation a prominent bacterial growth was noticed on Chocolate agar, Tryptic soy blood agar, and MacConkey agar plates (Novamed, Israel). The suspected bacterium was identified as V. cholerae by means of VITEK-2 bacterial identifier system (BioMerieux, France) and by using Vitek-MS MALDI-TOF technology (BioMerieux, France). Additionally, five single colonies were picked and streaked on Luria (LB) agar (HiMedia, Mumbai) in five successive days to verify the purity of the isolates; then their identities were verified by a PCR assay in accordance with Nandi et al. (2000). The results demonstrated that all the strains were positive for ompW, a gene of an outer membrane protein, specific to V. cholerae. The isolate was confirmed as V. cholerae non-O1/O139, cholera toxin-negative by the reference laboratory of the Israeli Ministry of Health. Somatic antigen serogrouping identification was employed on the five V. cholerae isolates according to Shimada et al. (1994), and all the isolates were identified as V. cholerae serogroup O100.
The isolates underwent complete antibiogram susceptibility testing by the disk diffusion technique (Oxoid, United Kingdom) with interpretation according to the V. cholerae CLSI guidelines (Clinical and Laboratory Standards Institute [CLSI], 2014). The strains proved resistant to polymyxin B sulfate and susceptible to co-amoxiclav, cefuroxime, co-trimoxazole, gentamicin, and ciprofloxacin. Based on the results of antibiotics activity against the isolates in vitro, ciprofloxacin ear drops were used until the patients symptoms disappeared completely. Three weeks later; an additional swab from his right ear was sent to our laboratory; it was found negative for V. cholerae.

DISCUSSION
Vibrio cholerae belongs to the class of environmental pathogens defined as microorganisms that normally spend a substantial part of their life cycle outside the human host but, when introduced into humans, cause disease with measurable frequency (Clemens et al., 2017). While serogroups O1 and O139 cause cholera, the non-O1/O139 serogroups can cause a milder diarrhea, and are also associated with various human infections: blood, wound, ear, and other clinical sites (Dalsgaard et al., 2000).
The patient described in the current case is an immunocompetent young male with no history of chronic ear infections before the water skiing accident in Australia, during which his eardrum was perforated. V. cholerae O1 and non-O1/O139 had been isolated from river and marine water over a wide area in Australia since 1977 (Desmarchelier et al., 1988), which may link the ear injury in the Australian river to the subsequent V. cholerae otitis media. The water skiing accident happened in January, which is summer in Australia. Water temperatures and V. cholerae population size in the aquatic environment usually are higher during this season. Summer months are also the most common months of non-O1/O139 V. cholerae infections (Chen et al., 2015).
The isolates identified in this study didn't harbor the virulence gene cassette such as the cholera toxin gene and the genes encoding Type Three Secretion System. Thus, these genes probably have no significant role in causing otitis media. On the other hand, the isolate harbored other virulence related genes, hlyA, hapA, toxR, and ompU. The pathogenic mechanisms of V. cholerae non-O1/139 in otitis media remain unclear, but these genes might play a role in the disease process. Using cytotoxicity and apoptosis assays, showed that hlyA-positive strains of V. cholerae non-O1/O139 had significantly higher cytotoxic activity and levels of apoptosis induction than hlyA-negative strains, and that a mitochondriadependent apoptosis pathway is involved (Kanoktippornchai et al., 2014).
Furthermore, V. cholerae O100 isolate in the current study was positive to toxR and ompU genes. ToxR is the master regulator of V. cholerae pathogenicity (Faruque et al., 1998). Among other pathogenic genes, it regulates OmpU, one of the major outer membrane proteins of V. cholerae (Miller and Mekalanos, 1988). ompU, which is an outer membrane porin, has a role in the passage of certain substances through the outer membrane. Also, it has been shown that ToxR controls resistance to various cationic antibacterial proteins, for example, polymyxin B sulfate, through a porinmediated mechanism (Mathur and Waldor, 2004). Indeed, in the current study, the isolates that were positive to toxR and ompU genes were resistant to polymyxin B sulfate antibiotics.
Moreover, OmpU is pro-inflammatory in nature. Interestingly, it can also down-regulate LPS (lipopolysaccharide)mediated proinflammatory responses. OmpU causes suppression of LPS-mediated responses by attenuating the LPS-mediated toll-like receptor signaling pathway (Sakharwade and Mukhopadhaya, 2015). The presence of OmpU protein in the bacterial isolate may explain the phenomenon that was observed in the current case in which the patient suffered from symptoms of earache and purulent exudate for three years. He was cured only when the bacteria was identified and treated with ciprofloxacin ear drops. This antibiotic treatment was effective and all the symptoms completely disappeared.
A few cases of otitis media or otitis externa caused by V. cholerae non-O1/O139 are reported in the literature. Most were children (n = 7, aged between 9 and 15 years) two young males and one female in their early twenties, and one 49 year- old-man ( Table 1). The majority of the reported cases were from European countries and only one report was from the United States. In seven cases it was reported that the patients had been swimming in a swimming pool, a lake or in the Baltic Sea. Untreated otitis media can cause complications such as loss of hearing, inner ear and facial nerve problems, including vertigo (Kitsko and Dohar, 2007), and extracranial and intracranial complications (Kangsanarak et al., 1993). Fortunately, the patient in the current case had not such complications. Nevertheless, physicians should be aware that non-O1/O139 V. cholerae can cause extra-intestinal infections that can be acquired from exposure to swimming pools and river, lake or marine water. Thus, V. cholerae should be added to the differential diagnosis of otitis infections.

AUTHOR CONTRIBUTIONS
PK, YS, and SL-S identified the strains. EA, serotyped the strains. SL-S identified the virulence genes. PK and YS performed the antibiogram tests. PK and YS wrote the manuscript, SK-D and MH reviewed the manuscript. MH Edited the manuscript. MH, Contributed reagents/materials/publication fee.