Objectives: High rates of carbapenem resistance in the human pathogen Acinetobacter baumannii threaten public health and need to be scrutinized. Methods: A total of 356 A. baumannii and 50 non-baumannii Acinetobacter spp. (NBA) strains collected in 2013 throughout South Korea were studied. The type of blaOXA-23 transposon was determined by PCR mapping and molecular epidemiology was assessed by MLST. Twelve representative strains and two comparative A. baumannii were entirely sequenced by single-molecule real-time sequencing. Results: The carbapenem resistance rate was 88% in A. baumannii, mainly due to blaOXA-23, with five exceptional cases associatedwith ISAba1-blaOXA-51-like. The blaOXA-23 gene in A. baumannii was carried either by Tn2006 (44%) or Tn2009 (54%), with a few exceptions carried by Tn2008 (1.6%). Of the NBA strains, 14% were resistant to carbapenems, twowith blaOXA-58 and five with blaOXA-23 associated with Tn2006. The Tn2006-possessing strains belonged to various STs, whereas Tn2008- and Tn2009-possessing strains were limited to ST208 and ST191, respectively. The three transposons were oftenmultiplied in the chromosome, and the gene copy number and the carbapenem MICs presented linear relationships either very strongly for Tn2008 ormoderately for Tn2006 and Tn2009. Conclusions: The dissemination of Tn2006 was facilitated by its capability for intercellular transfer and that of Tn2009 was attributable to successful dissemination of the ST191 bacterial host carrying the transposon. Tn2008 was infrequent because of its insufficient ability to undergo intercellular transfer and the scarce bacterial host A. baumannii ST208. Gene amplification is an adaptivemechanismfor bacteria that encounter antimicrobial drugs.
Bibliographical noteFunding Information:
We thank H. S. Lee (Yonsei University College of Medicine) for helpful statistical analysis advice. This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HI12C0756).
All Science Journal Classification (ASJC) codes
- Microbiology (medical)
- Infectious Diseases
- Pharmacology (medical)