Dissemination of blaOXA-23 in Acinetobacter spp. in China: main roles of conjugative plasmid pAZJ221 and transposon Tn2009

Antimicrob Agents Chemother. 2015 Apr;59(4):1998-2005. doi: 10.1128/AAC.04574-14. Epub 2015 Jan 20.

Abstract

Production of the OXA-23 carbapenemase is the most common reason for the increasing carbapenem resistance in Acinetobacter spp. This study was conducted to reveal the genetic basis of blaOXA-23 dissemination in Acinetobacter spp. in China. A total of 63 carbapenem-resistant OXA-23-producing Acinetobacter sp. isolates, representing different backgrounds, were selected from 28 hospitals in 18 provinces for this study. Generally, two patterns of plasmids carrying blaOXA-23 were detected according to S1-nuclease pulsed-field gel electrophoresis and Southern blot hybridization. A ca. 78-kb plasmid, designated pAZJ221, was found in 23 Acinetobacter baumannii and three Acinetobacter nosocomialis isolates, while a novel ca. 50-kb plasmid was carried by only two other A. baumannii isolates. Three of these isolates had an additional copy of blaOXA-23 on the chromosome. Transformation of the two plasmids succeeded, but only pAZJ221 was conjugative. Plasmid pAZJ221 was sequenced completely and found to carry no previously known resistance genes except blaOXA-23. The blaOXA-23 gene of the remaining 35 isolates was chromosome borne. The blaOXA-23 genetic environments were correlated with Tn2009 in 57 isolates, Tn2008 in 5 isolates, and Tn2006 in 1 isolate. The MIC values for the carbapenems with these isolates were not significantly associated with the genomic locations or the copy numbers of blaOXA-23. Overall, these observations suggest that the plasmid pAZJ221 and Tn2009 have effectively contributed to the wide dissemination of blaOXA-23 in Acinetobacter spp. in China and that horizontal gene transfer may play an important role in dissemination of the blaOXA-23 gene.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter / drug effects*
  • Acinetobacter / genetics*
  • Acinetobacter Infections / microbiology
  • Bacterial Proteins / genetics*
  • China
  • Chromosomes, Bacterial / genetics
  • Conjugation, Genetic / genetics*
  • DNA Transposable Elements / genetics*
  • DNA, Bacterial / genetics
  • Humans
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Plasmids / genetics*
  • beta-Lactamases / genetics*

Substances

  • Bacterial Proteins
  • DNA Transposable Elements
  • DNA, Bacterial
  • beta-Lactamases
  • beta-lactamase OXA-23, Acinetobacter baumannii