Molecular Epidemiology of Infection Caused by OXA-23 or IMP-1 beta-Lactamase-Producing Acinetobacter baumannii / 대한임상미생물학회지

ABSTRACT

BACKGROUND: The purposes of this study were to investigate the prevalence of imipenem-resistant clinical Acinetobacter baumannii isolates and to determine the mechanism of the resistance. METHODS: During the period of June to September 2004, susceptibility to imipenem of A. baumannii isolates from a hospital in Busan, Korea were investigated. The isolates were screened for the production of carbapenemase and metallo-beta-lactamase by Modified-Hodge and EDTA-disk synergy tests, respectively; minimum inhibitory concentrations (MICs) were determined by agar dilution method. Genes coding for GES, IMP, VIM, SMP-1, GIM-1 and OXA type beta-lactamases were searched by PCR amplification, and the PCR products were subjected to direct sequencing. Isoelectric points of beta-lactamases were estimated by isoelectric focusing and the epidemiological relationships of isolates were investigated by enterobacterial repetitive intergenic consensus (ERIC) PCR. RESULTS: Fifty eight strains of A. baumannii were isolated from clinical specimens during the surveillance period, and 14 isolates (24.1%) were resistant to imipenem. Of the 14 isolates, 9 were tested positive in Modified-Hodge test and 2 were also positive in EDTA-disk synergy test. Genes encoding OXA-23 and IMP-1 were detected in 7 and 2 isolates, respectively. In IEF studies, OXA-23 and IMP-1 enzymes had corresponding pIs at 6.7 and 9.0, respectively. Seven OXA-23-producing and 2 IMP-1-producing isolates showed the same ERIC PCR patterns. CONCLUSION: It is concluded that 7 and 2 A. baumannii isolates from the patients in a hospital in Busan acquired resistance to imipenem by producing OXA-23 and IMP-1 beta-lactamases, respectively. The isolates producing these beta-lactamases might be originated from a common source.