Objective: The aim of this study was to investigate the presence of metallo-beta-lactamase (MBL) enzymes responsible for imipenem resistance in Acinetobacter strains isolated from various clinical specimens, by phenotypical and genotypical methods.

Materials and Methods: Imipenem resistant 79 Acinetobacter spp. strains identified by automated identification system (VİTEK 2; bioMérieux, France) were included in the study. In order to determine fast, easy and reliable methods for the identification of MBLs in routine clinical microbiology laboratory, all strains in this study were subjected to four phenotypical tests which were E-test MBL, combined disc synergy test, double disc synergy test and modified Hodge test. The presence of bla_IMP-1 gene which coded the most frequent MBL enzyme in Acinetobacter strains was investigated by polimerase chain reaction (PCR) and clonal analysis was performed by pulsed field gel electrophoresis (PFGE).

Results: Among imipenem resistant Acinetobacter isolates were found to produce MBL by using E-test (n=41; 51.9%), combined disc synergy test (n=46; 58.2%), double disc synergy test (n=44; 55.7%) or modified Hodge test (n=55; 69.6%). The most compatible test with E test was combined disc synergy with a 75.9% compatibility. The bla_IMP-1 gene investigated by PCR yielded no positive result. Ten different band patterns were found by PFGE, and phenotypically MBL positive isolates were mostly clustered in A and C groups.

Conclusion: As combined disc synergy test showed highest compatibility with E-test, it can be suggested as an alternative for MBL detection in laboratories where E-test is not used. Genes other than bla_IMP-1 might be responsible for MBL production by Acinetobacter strains in our hospital. In order to limit spread of resistance and guide treatment, carbapenem resistance patterns should be determined and epidemiological analysis should be done in routine microbiology laboratories.