Selection of topoisomerase mutations and overexpression of adeB mRNA transcripts during an outbreak of Acinetobacter baumannii

J Antimicrob Chemother. 2004 Oct;54(4):821-3. doi: 10.1093/jac/dkh427. Epub 2004 Sep 8.


Objectives: To investigate the mechanism of ciprofloxacin resistance in isolates of Acinetobacter baumannii during two hospital outbreaks and to determine the expression level of the gene encoding the AdeB efflux pump.

Methods: Isolates were previously typed by PFGE and their MICs determined by broth microdilution. The gyrA and parC genes were sequenced and the adeB gene examined by real-time reverse transcription PCR (RT-PCR).

Results: Two clonal lineages were responsible for the two hospital outbreaks. In both outbreaks, ciprofloxacin susceptibility was reduced during the course of the outbreak when compared with the index isolates. Mutations in gyrA and parC were found to have occurred during the outbreak. The MICs of non-fluoroquinolone antibiotics were raised in one clonal lineage and this was associated with a >10-fold increase in mRNA transcripts for adeB.

Conclusions: We have witnessed the appearance of gyrA and parC mutations during outbreaks of A. baumannii. In parallel with these mutations, we observed up-regulation of the adeB gene associated with a decrease in susceptibility to non-fluoroquinolone antibiotics. These data illustrate the propensity for A. baumannii to develop multi-drug resistance rapidly.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter Infections / microbiology*
  • Acinetobacter baumannii / enzymology
  • Acinetobacter baumannii / genetics*
  • Acinetobacter baumannii / isolation & purification
  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / genetics*
  • Cross Infection / epidemiology
  • Cross Infection / microbiology
  • DNA Gyrase / genetics*
  • DNA Topoisomerase IV / genetics*
  • Disease Outbreaks*
  • Drug Resistance, Multiple, Bacterial / genetics
  • Humans
  • Membrane Transport Proteins / genetics*
  • Microbial Sensitivity Tests
  • Mutation
  • RNA, Messenger / genetics
  • Transcription, Genetic


  • AdeB protein, Acinetobacter baumannii
  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Membrane Transport Proteins
  • RNA, Messenger
  • DNA Topoisomerase IV
  • DNA Gyrase