title: Dissemination of imipenem-resistant Acinetobacter baumannii with new plasmid-borne bla(OXA-72) in Taiwan.
abstract: BACKGROUND
  The systemic surveillance of imipenem-resistant Acinetobacter baumannii (IRAB) from multicenters in Taiwan revealed the emergence of isolates with bla(OXA-72). This study described their genetic makeup, mechanism of spread, and contribution to carbapenem resistance.
  
  
  METHODS
  Two hundred and ninety-one non-repetitive isolates of A. baumannii were collected from 10 teaching hospitals from different geographical regions in Taiwan from June 2007 to September 2007. Minimal inhibitory concentrations (MICs) were determined by agar dilution. Clonality was determined by pulsed-field gel electrophoresis. Plasmid was extracted and digested by restriction enzymes, and subsequently analyzed by electrophoresis and Southern blot for bla(OXA-72). The flanking regions of bla(OXA-72) were determined by inverse PCR. The contribution of bla(OXA-72) to imipenem MIC was determined by transforming plasmids carrying bla(OXA-72) into imipenem-susceptible A. baumannii.
  
  
  RESULTS
  Among 142 IRAB in Taiwan, 27 harbored bla(OXA-72); 22 originated from Southern Taiwan, 5 from Central Taiwan, and none from Northern Taiwan. There were two major clones. The bla(OXA-72) was identified in the plasmids of all isolates. Two genetic structures flanking plasmid-borne bla(OXA-72) were identified and shared identical sequences in certain regions; the one described in previous literature was present in only one isolate, and the new one was present in the remaining isolates. Introduction of bla(OXA-72) resulted in an increase of imipenem MIC in the transformants. The overexpression of bla(OXA-72) mRNA in response to imipenem further supported the contribution of bla(OXA-72).
  
  
  CONCLUSIONS
  In conclusion, isolates with new plasmid-borne blaOXA-72 were found to be disseminated successfully in Southern Taiwan. The spread of the resistance gene depended on clonal spread and dissemination of a new plasmid. Bla(OXA-72) in these isolates directly led to their imipenem-resistance.
authors.affiliation: Institute of Clinical Medicine, National Yang-Ming University, School of Medicine, Beitou District, Taipei 112, Taiwan.
authors.forename: Shu-Chen
authors.initials: SC
authors.lastname: Kuo
authors.forename: Su-Pen
authors.initials: SP
authors.lastname: Yang
authors.forename: Yi-Tzu
authors.initials: YT
authors.lastname: Lee
authors.forename: Han-Chuan
authors.initials: HC
authors.lastname: Chuang
authors.forename: Chien-Pei
authors.initials: CP
authors.lastname: Chen
authors.forename: Chi-Ling
authors.initials: CL
authors.lastname: Chang
authors.forename: Te-Li
authors.initials: TL
authors.lastname: Chen
authors.forename: Po-Liang
authors.initials: PL
authors.lastname: Lu
authors.forename: Po-Ren
authors.initials: PR
authors.lastname: Hsueh
authors.forename: Chang-Phone
authors.initials: CP
authors.lastname: Fung
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015139:Blotting, Southern; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D012189:Retrospective Studies; D013624:Taiwan; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D015378:Imipenem; D001618:beta-Lactamases