Characterization of Oxacillinase and Metallo-β-Lactamas Genes and Molecular Typing of Clinical Isolates of Acinetobacter baumannii in Ahvaz, South-West of Iran

Carbapenem resistant Acinetobacter baumannii is an important nosocomial pathogen associated with a variety of infections.
The current study aimed to characterize the antimicrobial susceptibility, analyze the prevalence of oxacillinase and metallo-β-lactamase (MBL) genes and molecular typing of clinical isolates of A. baumannii.
A total of 124 non-repetitive isolates of A. baumannii were collected from various clinical specimens in two teaching hospitals in Ahvaz, south-west of Iran. Antimicrobial susceptibility test was carried out by disk diffusion method. The minimum inhibitory concentrations (MICs) of imipenem, meropenem, colistin and tigecycline were determined using E-test. To screen for MBL production, double disk synergy (DDs) test and MBL E-test were performed. The presence of blaOXA-23-like, blaOXA-24-like, blaOXA-51-like, blaOXA-58-like, blaVIM, blaIMP and blaSPM genes was assessed by polymerase chain reaction (PCR). To identify clonal relatedness, all isolates were subjected to repetitive sequence-based PCR (rep-PCR).
Based on disk diffusion results, the highest rate of resistance was observed in rifampin (96.8%). Colistin and polymyxin-B were the most effective agents in vitro. According to the MIC results, the rate of resistance to imipenem, meropenem, colistin and tigecycline were 78.2%, 73.4%, 0.8% and 0, respectively. Metallo-β-lactamase production was positive in 42.3% and 79.4% of the isolates by DDs test and E-test, respectively. All isolates (100%) carried blaOXA-51-like gene. According to the results of multiplex PCR, blaOXA-23-like and blaOXA-24-like genes were detected in 85.6% and 6.2% of carbapenem resistant isolates, respectively. No blaOXA-58- like, blaVIM, blaIMP and blaSPM were detected. By rep-PCR, carbapenem resistant isolates were separated into six genotypes (A to F). Genotype A (30.9%) was the most prevalent (P value The rate of carbapenem resistant A. baumannii isolates were high in this study. Since, blaOXA-58-like or MBL genes were not detected, it seems that resistance to carbapenems is related to blaOXA-23-like and blaOXA-24-like. Moreover, blaOXA-23-like was the most prevalent oxacillinase (OXA) gene. Most of the isolates belonged to one of the four dominant genotypes indicating clonal dissemination in the hospitals under study. In order to control the spread of carbapenem-resistant A. baumannii, infection- control strategies are needed.