Dissemination of multidrug-resistant Acinetobacter baumannii carrying BlaOxA-23 from hospitals in central Taiwan

BackgroundImipenem-resistant Acinetobacter baumannii (IRAB) poses a great threat to healthcare systems. Production of carbapenem-hydrolyzing class D β-lactamases (CHDLs) is the major mechanism for imipenem resistance. In this study, we found a high prevalence of IRAB carrying a gene encoding CHDL, blaOxA-23, in central Taiwan and elucidated the molecular characteristics and possible mechanisms of the spread of these isolates.MethodsDuring 2007, we collected 291 nonrepetitive A baumannii isolates from 10 teaching hospitals in Taiwan. The antimicrobial susceptibility of the isolates was determined by agar dilution or Etest. The genes encoding carbapenemase and related structure were detected by polymerase chain reaction mapping and sequencing, and the clonal relationship of the isolates was analyzed by pulsed-field gel electrophoresis. Plasmid localization of blaOxA-23 was determined by extraction of plasmid with commercial kit and Southern blot analysis.ResultsAmong 142 IRAB isolates, 30 harbored the blaOxA-23. The prevalence of IRAB with blaOxA-23 was highest in central Taiwan compared to other areas [24.8% (27/109) vs. 1.6% (3/182); p < 0.001]. These IRAB with blaOxA-23 were also resistant to other antimicrobial agents, except colistin. The PCR methods showed the presence of blaOxA-51 in all isolates. We could exclude clonal spreading due to the diversity of the pulsotype. The blaOxA-23 gene was detected in the plasmids of 6 isolates. Tn2006 was present in 22 (73.3%) isolates, and Tn2008, in 6 other isolates (26.7%). Two strains had blaoxa-23–ΔATPase but lacked upstream ISAba1.ConclusionThe high prevalence of blaOxA-23-harboring IRAB in central Taiwan might be attributed to the transposition event of Tn2006.