Carbapenem Resistance Mechanisms and Molecular Epidemiology of Acinetobacter spp. from Four Hospitals in Seoul and Gyeonggi Province in 2006

Background: Increasing numbers of Acinetobacter spp. resistant to multiple drugs, including carbape- nem, has been a serious problem. The aims of this study were to determine carbapenem resistance pat- terns and mechanisms, as well as to study the mo- lecular epidemiology of Acinetobacter spp. Methods: Clinical isolates of Acinetobacter spp. were collected from May to November in 2006. Antimicro- bial susceptibility testing was performed using CLSI disk diffusion and agar dilution methods. Metallo-β- lactamase- and OXA carbapenemase-producing iso- lates were detected by PCR. Carbapenem resistance and hydrolytic activities were compared according to OXA type and presence of ISAba1. Pulsed-field gel electrophoresis (PFGE) was performed to determine the epidemiologic features. Results: The imipenem non-susceptible rates were variable from 10% to 67%. Among 151 isolates car- rying blaOXA-51-like, 75 isolates carried both blaOXA-51-like and ISAba1, and 25 isolates had both blaOXA-51-like, blaOXA-23-like, and ISAba1. Carbapenem MICs of both blaOXA-51-like and ISAba1-carrying isolates were higher than those with blaOXA-51-like only. Carbapenem MICs of blaOXA-23-like-carrying isolates were higher than those with both blaOXA-51-like and ISAba1. Both blaOXA-51-like and ISAba1-carrying isolates and blaOXA-51-like, blaOXA-23-like, and ISAba1-carrying isolates demonstrated higher hydrolysis activities in oxacillin and carbapenems. Most of the tested isolates were susceptible to tige- cycline, and all of them were susceptible to colistin. Pulsed-field gel electrophoresis suggested that there had been several outbreaks of blaOXA-23-like and blaOXA-51-like-positive strains. Conclusion: Carbapenem non-susceptible Acineto- bacter isolates and OXA carbapenemase-producing isolates were prevalent. Dissemination of blaOXA-har- boring isolates may make it difficult to treat infections due to carbapenem-resistant Acinetobacter spp. Further surveillance studies are required to prevent the spread of carbapenem resistance. (Korean J Clin Microbiol 2010;13:27-33)