The epidemiology and antibiotic resistance in A. baumannii isolates from military health care facilities

Abstract

A.baumannii is one of the main causers of health care associated infections. The epidemiological situation has worsened in the past years, with a higher number of countries reporting interregional spread or endemicity of carbapenem-resistant A.baumannii. For these reasons to investigate epidemiology and susceptibility to antibiotics of A.baumannii in modern war wounds is crucial for correct treatment choice. The patients enrolled in study had combat wounds of upper or lower extremities which were treated in the Military Medical Clinical Center of Central Region (MMCC CR) Ukraine in 2014-2016 years. The recovered A.baumannii after primary identification in Department of Microbiology of National Pirogov Memorial Medical University were forwarded to the Multi-drug resistant repository and surveillance network (MRSN) in Walter Reed Army Institute of Research where they underwent additional antibiotic susceptibility testing (AST) and analysis by whole genome sequencing (WGS). There were analyzed 10 isolates. Testing revealed that all isolates were resistant to ampicillin, cefazolin, ciprofloxacin, and levofloxacin and all were sensitive to tigecycline. Susceptibility to other antibiotics varied considerably, with just two isolates displaying resistance to the carbapenems (imipenem and meropenem). An analysis of the antibiotic resistance genes carried by the isolates was in broad agreement with the AST data. Carbapenem resistance in VNMU001 was correlated with the presence of blaOXA-23, while carbapenem resistance in VNMU133 was correlated with the blaOXA-24 variant, blaOXA-72. Overall, 28 different antibiotic resistance genes were identified among the 10 isolates, with the majority encoding β-lactamases or aminoglycoside modifying enzymes (AMEs). The ten A. baumannii isolates represent four separate clades that include a single isolate from ST-1 and ST-2, members of the globally distributed CCI and CCII groups. Both of these clades are notorious for harboring multi-drug resistant strains, and this is reflected in this study where VNMU133 (CCI) and VNMU001 (CCII) displayed resistance to a wide variety of antibiotics and carried multiple antibiotic resistant genes. The remaining 8 isolates were assigned to ST-19, which is also a member of CCI, and all four isolates were closely related. Similarly, the four isolates from ST-400 clustered together, but only the two isolates from the same culture would be considered related. It is possible that ST-19 and ST-400 isolates are circulating within this population and additional surveillance is warranted. These data indicate that ST-19 and ST-400 isolates are still susceptible to many antibiotics but have the potential to acquire and develop more resistance mechanisms.