Investigation of class-d beta-lactamases causing carbapenem resistance in clinical Acinetobacter baumannii isolates.

Background/aim: Acinetobacter baumannii is an important causative agent of nosocomial infections, and carbapenems have been frequently used in the treatment of these infections. This study was designed to investigate the prevalence of primary carbapenem hydrolyzing oxacillinase (CHO) types in clinical A. bumannii strains. Materials and methods: Minimum inhibitory concentration (MIC) values of 76 imipenem nonsusceptible A. baumannii strains, isolated from a tertiary care hospital, were determined by microdilution method. The clonal relationship of the isolates was analyzed with enterobacterial repetitive intergenic consensus (ERIC)-PCR, and the presence of CHO major groups (OXA-23; OXA-24, OXA-51, and OXA-58 groups) was investigated with multiplex PCR. Results: According to the ERIC-PCR patterns, the isolates were distributed in 13 different clones, the largest of which had 40 members. blaOXA-51-group was detected in representatives of all clones, whereas blaOXA-23-group was detected in representatives of all but two small clones. Additionally, the presence of blaOXA-58-group was discovered in the members of two small clones, whereas blaOXA-24-group was not encountered in any of the examined strains. Conclusion: Molecular fingerprinting revealed that most imipenem-resistant A. baumannii strains were clonally related. blaOXA-23-group and blaOXA-51-group were mostly responsible for the imipenem resistance of the examined A. baumannii strains.