Based on the multicriteria decision analysis technique, WHO experts—together with researchers from the Comprehensive Infectious Disease Center Tübingen (CIDiC) at the University of Tübingen, Germany—published a list of “priority pathogens” – 12 species of bacteria that pose the greatest threat to human health (2017). This list was prepared as a part of the efforts by the WHO to combat the increasing momentum of antimicrobial resistance worldwide. According to the necessity of developing new strategies for resistance mitigation and creating new antibiotics, the bacteria on this list are divided into extremely high priority (critical priority group), high priority, and medium priority. Acinetobacter, Pseudomonas, and various species of the family Enterobacteriaceae (including E. coli, Klebsiella spp., Serratia, and Proteus) were included in the group of critical priority. These bacteria have developed resistance to a wide range of antibiotics, including carbapenems and third-generation of cephalosporins, which are considered reserve antibiotics among the available antibiotics for the treatment of multidrug-resistant bacterial infections (World Health Organization [WHO], 2017; Centers for Disease Control and Prevention [CDC], 2019; Talebi Bezmin Abadi et al., 2019).

Carbapenem-resistant A. baumannii was classified as the most serious menace in the “critical group” of priority. This non-fermenting gram-negative bacterium is a major cause of severe infections associated with medical care, such as pneumonia associated with pulmonary ventilation (artificial lung ventilation), bloodstream infections, bacteremia, urinary tract infections, and wound infections, especially in patients with burns and postoperative pains (Gheorghe et al., 2021; Sloczynska et al., 2021). During war, the impact of A. baumannii on the development of combat wound infections and other infections has been reported previously (Calhoun et al., 2008).

In this context, with increasing resistance of A. baumannii toward reserve antibiotics, such as carbapenems and polymyxins, therapeutic possibilities are very limited or absent in some cases of infections caused by bacteria with pan-antimicrobial resistance. This situation encourages researchers worldwide to seek and study new therapeutic strategies as an alternative to antibiotics (Fournier et al., 2006; Kempf and Rolain, 2012; Thomas et al., 2019; Ibrahim et al., 2021; Lin et al., 2021; Park et al., 2021; Pimentel et al., 2021; Shahid et al., 2021; Sloczynska et al., 2021).

In addition, a significant correlation between multidrug resistance and biofilm formation of A. baumannii clinical isolates was established (Han et al., 2014; Kim et al., 2015; Dafopoulou et al., 2016; de Campos et al., 2016; Duarte et al., 2016; Qi et al., 2016; Zhang et al., 2016; Bardbari et al., 2017). Developing biofilm-specific countermeasures is a step toward limiting and containing biofilm-associated infections (Han et al., 2014; Kim et al., 2015; Dafopoulou et al., 2016; de Campos et al., 2016; Duarte et al., 2016; Qi et al., 2016; Zhang et al., 2016; Bardbari et al., 2017).

Effective management of bacterial bioload is an important element of wound care, as any injury is characterized by a high probability of infection. The use of antiseptics to combat colonization and infection directly at the portal of entry is a vital step in preventing further infectious complications. Antiseptics are defined as antimicrobial substances that are non-damaging to living tissue/skin while reducing the possibility of infection, sepsis, or putrefaction. Among the variety of antiseptic preparations, ñationic surfactants (CSs) and complex compounds of iodine and the synthetic polymer polyvinylpyrolidone (povidone-iodine) deserve special attention. Because of their important properties, such as the non-selectivity of the antimicrobial effect on the bacterial cell, sufficient biological safety, lack of toxic effect, and weak irritating effect on the skin, mucous membranes, and tissues of wound surfaces, CSs are considered the most promising (Junka et al., 2014; Alvarez-Marin et al., 2017; Davis et al., 2017; Hoekstra et al., 2017; Santos et al., 2017; Shepherd et al., 2018; Htun et al., 2019; Jeronimo et al., 2020; Huang et al., 2021; Krasowski et al., 2021; Lin et al., 2021; Loose et al., 2021).

This work studied the antimicrobial activity of antiseptics against planktonic bacterial forms and biofilm formation of multidrug-resistant clinical strains of A. baumannii isolated from combat wounds with infectious and inflammatory complications.

Healthcare-associated infections (HCAIs) are among the most prominent medical problems worldwide. The US Center for Disease Control and Prevention identifies that nearly 1.7 million hospitalized patients annually acquire HCAIs while being treated for other health issues and that more than 98,000 patients (one in 17) die due to these (Hoekstra et al., 2017).

The rapidly evolving nature of A. baumannii multidrug-resistant strains is a cause of concern. It accounts for approximately 2–10% of all gram-negative hospital-acquired infections in intensive care units (Calhoun et al., 2008). In 2017, carbapenem-resistant Acinetobacter caused an estimated 8,500 infections in hospitalized patients and 700 estimated deaths in the USA (Centers for Disease Control and Prevention [CDC], 2019).

In the context of a global increase in antibiotic resistance, the use of antiseptics as the main active agent and potentiator of antibiotics is of great importance for treating patients with infected post-traumatic and surgical wounds and burns (Kempf and Rolain, 2012; Thomas et al., 2019; Lin et al., 2021; Park et al., 2021). In this study, the inhibitory and bactericidal effects of the selected antiseptics on A. baumannii planktonic and biofilm-forming states were evaluated.

Maillard et al. (2021) reviewed previous studies of susceptibility to modern antiseptics and reported decreased biocide susceptibility for all biocides. So far, planktonic forms of A. baumannii have shown only a weak adaptive or no response to chlorhexidine, octenidine, polyhexanide, and povidone-iodine. The MIC and MBC values of antiseptics are known to differ, increasing in the presence of multidrug-resistant isolates. In the case of A. baumannii, such a probability of variability has prompted us to research strains isolated from combat burn wounds from different localizations. Our study found a fairly high in vitro efficacy of the tested antiseptics, which are commonly used.

The MIC and MBC values of quaternary ammonium compound (QAC) antiseptics, such as decamethoxine and octenidine, showed that they were the most effective drugs. For QAC and halogen compound antiseptics, as their IAA (BS and BC) was >4, they were considered active. The ratio of BC to BS IAAs varied between 0.47 and 0.5 for QAC antiseptics. For different concentrations of povidone-iodine, this ratio was 0.70, demonstrating that it had the highest bactericidal effect.

Index of antiseptic activity (IAA) values were highest (IAA > 4) for the antiseptics decamethoxine (0.1%), octenidine (0.1%), and povidone-iodine (10%), which correlated with high concentrations of active substances in the initial working solutions of these drugs. On the other hand, 0.02% decamethoxine, 0.05% chlorhexidine, and 0.1% polyhexanide exhibited lower IAA values; however, their BS and BC IAA values exceeded the threshold (4) by 5.05–7.4 times and 2.53–4.0 times, respectively; these concentrations were effective against multidrug-resistant A. baumannii. On the contrary, the effectiveness of 0.01% miramistin against multidrug-resistant A. baumannii was found insufficient (BS IAA = 3.8; BC IAA = 1.9, both < 4). The feasibility of using 1.0% povidone-iodine is questionable as the BS IAA (=5.6) is above the threshold value, while the BC IAA (=3.9) is not. In order to avoid creating selective conditions for the emergence of resistant strains, it may be appropriate to use concentrations of povidone-iodine of no less than 2%.

The results of the current study are largely consistent with those from other countries. Many researchers have reported a decrease in the susceptibility of many microorganisms to chlorhexidine (Saleem et al., 2016; Maya et al., 2021; Leshem et al., 2022). Leshem et al. (2022) demonstrated reduced susceptibility of gram-negative bacteria, including A. baumannii, to chlorhexidine but, at the same time, emphasized that none of these isolates appeared to be chlorhexidine-tolerant based on their MIC values. Another study showed the effectiveness of chlorhexidine and povidone-iodine against 81 A. baumannii isolates. However, 18.51% of the isolates were resistant to one-third of diluted povidone-iodine (Lanjri et al., 2017). A study by López-Rojas et al. (2017) highlighted that polyhexanide demonstrated bactericidal activity against all high-risk clones of multidrug-resistant nosocomial pathogens (including A. baumannii) at significantly lower concentrations and times of activity than those commercially used. The usefulness of octenidine for eradicating emergent, highly resistant Gram-negative nosocomial pathogens has been previously reported (Alvarez-Marin et al., 2017).

Increased tolerance of biofilms toward antimicrobials and their involvement in recurring infections has prompted the development of anti-biofilm strategies (Maillard et al., 2021). Therefore, the second part of this study aimed to evaluate the ability of commercially available antiseptics to prevent biofilm formation. QAC antiseptics and the halogenated compound antiseptic, povidone-iodine, exhibited different effects on the formation stage of A. baumannii biofilms. Previously, chlorhexidine and octenidine were found to possess the greatest efficacy against mature biofilms of clinical multidrug-resistant microorganisms, including A. baumannii (Günther et al., 2021). We investigated the effect of antiseptics on immature biofilms to prevent their formation. Our study also confirms that chlorhexidine had the highest antibiofilm activity against clinical isolates.

In the presence of sub-bacteriostatic chlorhexidine concentrations, our clinical strains’ biofilm-forming properties negatively correlated with their susceptibility to this antiseptic (r = 0.15). Owing to the significant inhibition of biofilm formation and the positive correlation of this property with the susceptibility of A. baumannii isolates toward this antiseptic, chlorhexidine should be considered an effective agent. Sub-bacteriostatic concentrations of decamethoxine significantly inhibited biofilm formation. This property was inversely correlated with the decamethoxine susceptibility of the strains (r = –0.76). Thus, the biofilm-forming activity of A. baumannii strains was inversely proportional depending on the concentration of the said antiseptic used. Analyzing the obtained results, we can see that bacteriostatic and higher concentrations of decamethoxine can provide reliable protection against biofilms.

Sub-bacteriostatic concentrations of octenidine, polyhexanide, miramistin, and povidone-iodine showed a low anti-biofilm-forming effect in A. baumannii, and the difference relative to the control was not statistically significant. A strong negative correlation between the biofilm-forming properties of A. baumannii in the presence of sub-bacteriostatic concentrations of these mentioned antiseptics and their susceptibility toward them indicates the dependence of these properties on antiseptic concentration, not on the increased susceptibility of individual strains. The correctness of our interpretation is confirmed by the studies of Loose et al. (2021) where octenidine and polyhexanide prevented biofilm formation in Escherichia coli, Pseudomonas aeruginosa, and Proteus mirabilis, depending on antiseptic concentration (Loose et al., 2021). Moreover, 0.25% (w/w) of povidone-iodine completely eradicated the biofilms of all multidrug-resistant microorganisms (Capriotti et al., 2018). It follows that the use of these QAC antiseptics in concentrations lower than MIC may stimulate the protective mechanisms of bacteria, as well as biofilm formation, which needs further research.

According to previous literature (Qi et al., 2016), a higher risk of biofilm formation is closely associated with multi-resistant strains of A. baumannii than with susceptible ones since the ability to form a biofilm is an important factor of resistance. At the same time, the relationship between the biofilm formation of antibiotic-resistant clinical strains of bacteria and their susceptibility to antiseptics has not yet been clearly established (Babapour et al., 2016; Bardbari et al., 2017; Guo and Xiang, 2017; Hall and Mah, 2017; Haque et al., 2018). Our research found a similar pattern for clinical strains of A. baumannii. A statistically negative correlation was found between the susceptibility to antiseptics of studied antibiotic-resistant clinical strains and their biofilm-forming capacity in the presence of sub-MIC levels of the studied antiseptics (except for chlorhexidine).

Previous research from different countries and time periods has also dealt with the problem of wound infection, its causative agents, and the effectiveness of modern antiseptics against leading wound pathogens. Different approaches and methods were used to achieve these goals (Koburger et al., 2010; Shen et al., 2011; Abdeyazdan et al., 2014; Amalaradjou and Venkitanarayanan, 2014; Kovalchuk et al., 2014; Günther et al., 2015; Lefebvre et al., 2016; Bukhary and Balto, 2017; Gunther et al., 2017; Hoekstra et al., 2017; Kittinger et al., 2017; Johani et al., 2018; Machuca et al., 2019; Krasowski et al., 2021). An important task for us is to monitor wound pathogens in our country during wartime and analyze the effectiveness of available antiseptics against them. Given the increasingly global spread of antibiotic resistance, the susceptibility of various microorganisms to biocides may constantly change. Thus, a comprehensive study of the antimicrobial action of antiseptics, a detailed analysis of the obtained data, and a study of the experience of researchers from different countries are necessary to fight against infectious complications of wounds and burns.

Modern surfactant-active antiseptics include decamethoxine, chlorhexidine, octenidine, polyhexanide, and halogenated compound povidone-iodine (10 and 2%), which provide effective antimicrobial activity against planktonic multidrug-resistant A. baumannii clinical strains colonizing combat wounds and burns, while miramistin (0.01%) was not effective. Sub-bacteriostatic concentrations of decamethoxine and chlorhexidine reliably inhibited the formation of biofilms by clinical strains of A. baumannii that colonized combat wounds (p < 0.001). The high antibiofilm-forming properties of chlorhexidine that are positively correlated with the susceptibility of A. baumannii to this antiseptic demonstrate its effectiveness against biofilm formation. In terms of both bactericidal properties and inhibition of biofilm formation, chlorhexidine and decamethoxine are the most effective of all tested antiseptics.

The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/supplementary material.

TD, NB, DD, and VB performed the antibacterial activity determination and were involved in the review of the literature. ON and RC were involved in collecting microbial cultures. TD, ON, OG, and RC designed the study, wrote the manuscript, participated in the data analysis, and provided critical manuscript revisions for valuable intellectual content. All authors contributed to the interpretation of the results, the revision of the draft manuscript, and the approval of the final version.