Investigation of Metallo Beta Lactamases and Oxacilinases in Carbapenem Resistant Acinetobacter baumannii Strains Isolated from Inpatients

Background: Resistance to beta-lactam antibiotics is widespread among Acinetobacter strains. Plasmid-mediated metallo beta lactamases (MBL) are responsible for carbapenem resistance, as are oxacillinases (OXA). In recent years, MBL producing carbapenem-resistant strains have been reported in the world and in Turkey in increasing rates. In our country, besides the OXA 51-like enzyme which is inherent in A. baumannii strains, OXA 58-like and OXA 23-like carbapenemases producing strains have also been widely detected. In addition, Verona Imipenemase (VIM) and (IMP)-type MBL have been reported in some centers. Aims: The aim of our study was to investigate the presence of carbapenemases in Acinetobacter strains isolated from hospitalized patients in Edirne. Study Design: Cross-sectional study. Methods: A total of 52 imipenem-resistant A. baumannii strains isolated between January and March 2013 were investigated. The presence of MBL was described phenotypically by the combined disk diffusion test (CDDT), double disk synergy test (DDST), MBL Etest (only performed in 28 strains) and modified Hodge test. bla(IMP), bla(VIM), bla(GIM), bla(SIM), bla(SPM) genes and bla(OXA-23), bla(OXA-51), bla(OXA-40), bla(OXA-58) genes were investigated by multiplex polymerase chain reaction (PCR). The blaNDM-1 gene was determined by PCR. Results: By modified Hodge test, 50 strains (96%) were found to be MBL positive. Positivity of MBL was 21% by both CDDT (0.1 M EDTA) and DDST. Twenty-four of 28 strains (85.7%) were positive by MBL E-test. OXA 23-like and OXA 51-like carbapenemases were detected in all strains, but OXA 58-like and OXA 40-like carbapenemases-producing A. baumannii were not detected. Also, MBL genes were not detected by genotypic methods. Conclusion: Only OXA 23-like carbapenemase was responsible for carbapenem resistance in carbapenem-resistant Acinetobacter strains in Edirne. The MBL-producing Acinetobacter strain is not yet a problem in our hospital. MBL resistance was found by phenotyping tests, which must be confirmed by genotypic methods; multiplex PCR tests can be easily used for screening MBL.