Investigation of Metallo-Beta-Lactamases Production and IMP-1 and VIM-1 Type Genes in Acinetobacter baumannii Strains

Introduction: Detection of metallo-beta-lactamase (MBL) resistance genes in Acinetobacter baumannii strains is important due to transfer of resistance genes to other bacteria in the hospital environment. The aim of this study was to investigate metallo-beta-lactamases production in A. baumannii strains isolated from bloodstream infections and then to investigate IMP-1 and VIM-1 type genes in positive strains using phenotypic methods. Materials and Methods: A total of 100 strains isolated from blood cultures and identified as A. baumannii using the Microscan Walkaway (Dade Behring, West Sacramento, CA, USA) automated system were included in the study. The species identification was confirmed by hemolysis features on blood agar, lactose fermentation on Eosin Methylene Blue agar, catalase, oxidase, indole reactions, and growth at 44°C. Antimicrobial susceptibility tests were performed by disk diffusion. Colistin susceptibility interpretation was performed according to the British Society for Antimicrobial Chemotherapy criteria. Susceptibility test for imipenem, meropenem, ampicillin/sulbactam, cefoperazone/sulbactam, and tigecycline was performed by E-test (AB Biodisk, Solna, Sweden). The MBL production was investigated with combined disk test, modified Hodge test (MHT), and E-test methods. The strains that were positive for MBL based on phenotypic tests were investigated further for blaVIM-1 and blaIMP-1 by polymerase chain reaction (PCR). Results: Multidrug resistance was found in 99 of the 100 isolates included in the study, and the resistance rates for imipenem and meropenem were found as 66% and 76%, respectively. Colistin resistance was not detected, and minimum inhibitory concentration 50 (MIC50) and minimum inhibitory concentration 90 (MIC90) for tigecycline were 1 and 2 µg/mL, respectively. MBL production was found to be 54% by imipenem/imipenem-EDTA combination, 59% by meropenem/meropenem-EDTA combination, 54% by MHT, and 51% by E-test. The blaIMP-1 and blaVlM-1 genes were detected in 15 and 3 of these strains by PCR, respectively. Conclusion: In this study, IMP-1 and VIM-1 type genes were shown in 18 of 45 A. baumannii strains of MBL as determined with three phenotypic methods. This is a potential threat not only for causing resistance to carbapenems in A. baumannii strains but also for transfer resistance to Enterobacteriaceae by mobile genetic elements. Effective surveillance programs for detection of MBLs are essential to guide infection control programs in order to prevent further spread of resistant germs.