Emergence of multidrug resistance and metallo-beta-lactamase producing Acinetobacter baumannii isolated from patients in Shiraz, Iran

Background: Metallo-beta-lactamase (ML) enzymes production is one of the most important resistance mechanisms against carbapenems in some bacteria including Acinetobacter baumannii. Aims: This study was aimed to determine the antimicrobial susceptibility and the prevalence of ML among carbapenem-resistant isolates of A. baumannii. Materials and Methods: In this cross-sectional study from October 2012 to April 2013, 98 isolates were identified as A. baumannii using Microgen kits and confirmed by molecular method. These isolates were tested for antimicrobial susceptibilities by disk diffusion method according to the Clinical and Laboratory Standards Institute guidelines. Carbapenem-resistant isolates were further detected phenotypically by ML minimal inhibitory concentration (MIC)-test strips, and subsequently positive ML isolates were confirmed by polymerase chain reaction (PCR). Results: Overall, 98% (96/98) of A. baumannii isolates were detected as carbapenem-resistant by MIC test. Highest sensitivity to the tested antibiotic with 42.9% (42/98) was observed to colistin. Of 96 carbapenem-resistant isolates, 43 were phenotypically positive for ML; out of 43 isolates, 37 were confirmed for the presence of ML genes by PCR. Conclusion: The frequency of drug resistance among the clinical samples of A. baumannii isolated in our study against most of the antibiotics was very high. Moreover, all ML producing isolates were multidrug resistance. Therefore, systematic surveillance to detect ML producing bacteria and rational prescription and use of carbapenems could be helpful to prevent the spread of carbapenem resistance.