Molecular characterization of carbapenem-resistant Acinetobacter baumannii isolates causing bloodstream infections in intensive care unit

Abstract

Objective: In this study, the aim was to investigate the clonal relationship between carbapenem resistant Acinetobacter baumannii isolates and carbapenem resistance genes isolated from blood samples of patients followed in intensive care units by molecular methods. Methods: Bactec 9240 system (Becton Dickinson, USA) was used for the isolation of bacteria from blood culture flasks. Identification of 112 strains included in the study were performed by conventional tests, API 20NE (bioMerieux, France) and Phoenix TM 100 system (Becton Dickinson, USA) and confirmed by the presence of blaOXA-51 gene. Antimicrobial susceptibility tests were performed by Kirby-Bauer disk diffusion method and Phoenix TM 100 system. Carbapenem resistance genes; blaOXA-23, blaOXA-48, blaOXA-58, blaIMP, blaVIM and blaNDM-1 were investigated by Multiplex Polymerase Chain Reaction (PCR) method. Pulsed Field Gel Electrophoresis (PFGE) was used to determine the clonal relationship between Acinetobacter baumannii strains. Results: The antibiotic resistance percentages of strains for gentamicin, amikacin, tobramycin, netil micin, ceftazidime, trimethoprim/sulfamethoxazole, piperacillin, ciprofloxacin, ampicillin/sulbactam, piperacillin/tazobactam and cefoperazone/ sulbactam, were 88%; 81%; 78%; 36%; 98.5%; 96%; 89%; 100%; 100%; 93%; 91% respectively. MIC values of imipenem and meropenem were determined above ≥8 μg/ml in the whole group. blaOXA-51 and blaOXA-23 genes were detected in all isolates included in the study. By PFGE method, 62 different pulsotypes were detected. Among the pulsotypes, 19 of them contained ≥2 strains. It was observed that 108 (96.4%) strains were clustered in 11 clonally related groups when the similarity between pulsotypes for grouping was limited to 85% or more. Conclusion: In this study, it was observed that carbapenem-resistant A. baumannii strains were resistant for all tested antibiotics at high levels except netilmicin and spread in the hospital via cross contamination. These strains posed a risk for hospital infections, however, clonal-related strains were not limited to a specific unit and time period.