Carbapenem-resistant Acinetobacter baumannii: Current status of the problem in four Bulgarian university hospitals (2014-2016).

OBJECTIVES: A total of 226 carbapenem-resistant Acinetobacter baumannii (CRAB) isolates was collected during 2014-2016 from in-patients aged 5-88 years in four Bulgarian university hospitals (H1-H4), to assess their antimicrobial susceptibility and to explore carbapenem resistance mechanisms, as well as the molecular epidemiology.

METHODS: Antimicrobial susceptibility testing, multiplex polymerase chain reaction (PCR) assay, DNA sequencing, and electrotransformation experiments were performed. Epidemiological typing by Random amplified polymorphic DNA-PCR was also carried out.

RESULTS: The antibiotic resistance rates were: to imipenem - 90.7%, meropenem 98.3%, doripenem 100%, amikacin 92.9%, gentamicin 87.2%, tobramycin 55.7%, levofloxacin 98.2%, trimethoprim-sulfamethoxazole 86.3%, tigecycline 22.1%, colistin 0%, and ampicillin-sulbactam 41.6%. Intrinsic blaOXA-51-like genes were found in all isolates. The majority of strains harbored blaOXA-23-like associated with the upstream-located ISAba1 (26.1%) or blaOXA-40/24-like (46.7%) genes, forty-five A. baumannii (19.9%) - both genes, and one isolate contained blaOXA-58-like surrounded by ISAba3C (upstream) and ISAba3 (downstream). The blaOXA-58 gene was transferable by electroporation indicating its plasmid location. Epidemiological typing revealed the dissemination of nosocomial CRAB with high clonal relatednesss (threshold of 70% similarity) belonging to six, four, three and two clusters in H1, H2, H3, and H4, respectively.

CONCLUSIONS: A. baumanii isolates we studied were problematic nosocomial pathogens. Their multidrug resistance (MDR) poses great limits for therapeutic options. The persistence of endemic clones comprised of OXA carbapenemase-producing MDR A. baumannii in the monitored hospitals over a period of approximately three years is of concern and requires continuous detailed investigations in the future.