Usefulness of phenotypic and genotypic methods for metallo-beta-lactamases detection in carbapenem-resistant Acinetobacter baumannii strains

BACKGROUND: Acinetobacter baumannii is an opportunistic microorganism with an increasing role in nosocomial outbreaks. For the last 2 decades, a growing number of carbapenem-resistant A. baumannii strains have been identified, including the metallo-beta-lactamases (MBLs) producers. The study aimed to investigate the genetic relatedness of, and MBLs production among, a collection of A. baumannii isolates from Poland. MATERIAL/METHODS: This study involved 78 clinical isolates of carbapenem-resistant A. baumannii. Strain typing of the isolates was performed using PCR-RAPD. The presence of MBLs was phenotypically determined using different double disc synergy tests (DDST), the imipenem/EDTA combination disk test (CDT) and Etest MBL. bla(IMP) and bla(VIM) genes were detected using a duplex PCR assay. RESULTS: The isolates were divided into 18 PCR-RAPD patterns. Among 18 examined isolates, 94.4% were MBL-positive by the phenotypic method relying on comparing the bacteria growth inhibition zones diameters between imipenem/EDTA and imipenem discs, 88.9% using Etest MBL, 66.7% using the double disc synergy test with ceftazidime, imipenem, meropenem and EDTA, and 88.9% using a corresponding method with 2-MPA. The existence of bla(IMP) was identified in 8 (10.3%) strains. CONCLUSIONS: MBLs production was an important mechanism of carbapenem resistance among A. baumannii isolates in Poland. Laboratories should routinely screen for MBLs among A. baumannii isolates.