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

A total of 226 carbapenem-resistant Acinetobacter baumannii (CRAB) isolates was collected during 2014-2016 from inpatients (age range 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 of the isolates.

Antimicrobial susceptibility testing, multiplex PCR, DNA sequencing and electrotransformation experiments were performed. Epidemiological typing by random amplification of polymorphic DNA (RAPD)-PCR was also performed.

The resistance rates were as follows: imipenem, 90.7%; meropenem, 98.2%; doripenem, 100%; amikacin, 92.9%; gentamicin, 87.2%; tobramycin, 55.8%; levofloxacin, 98.2%; trimethoprim/sulfamethoxazole, 86.3%; tigecycline, 22.1%; colistin, 0%; and ampicillin/sulbactam, 41.6%. Intrinsic bla_OXA-51-like genes were found in all of the isolates. The majority of the A. baumannii isolates harboured either bla_OXA-23-like associated with the upstream-located ISAba1 (26.1%) or bla_{OXA-40/24-like} (46.7%), 45 isolates (19.9%) harboured both genes, and 1 isolate harboured bla_OXA-58-like surrounded by ISAba3C upstream and ISAba3 downstream. The bla_OXA-58 gene was transferable by electroporation indicating its plasmid location. Epidemiological typing revealed the dissemination of nosocomial CRAB with high clonal relatedness (70% similarity threshold) belonging to six, four, three and two clusters in H1, H2, H3, and H4 hospitals, respectively.

The A. baumannii isolates studied were problematic nosocomial pathogens. Their multidrug resistance greatly limits therapeutic options. The persistence of endemic clones comprised of OXA carbapenemase-producing multidrug-resistant A. baumannii in the monitored hospitals over a period of ca. 3 years is of concern and requires continuous detailed investigations in the future.