Characterization of fluoroquinolone resistance mechanisms and their correlation with the degree of resistance to clinically used fluoroquinolones among Escherichia coli isolates

J Chemother. 2007 Oct;19(5):488-94. doi: 10.1179/joc.2007.19.5.488.


DNA sequencing and real-time PCR were used to evaluate the gyrA and parC mutations, AcrAB efflux pump over-expression, and their correlation with high-level resistance to fluoroquinolones in 74 fluoroquinolone-resistant clinical Escherichia coli isolates recently collected in Taiwan. RAPD analysis revealed high clonal diversity. Isolates with four to five mutations (especially Ser83Leu, Asp87Asn [or Asp87Tyr], and Ala93Thr in gyrA and Ser80Ile and Glu84Gly in parC) had increased resistance levels. The acrA gene was over-expressed in 51% of 74 resistant isolates. The trend was towards increased fluoroquinolone MICs in isolates with both multiple mutations in the quinolone-resistance determining region (QRDR) and over-expression of the AcrAB efflux pump. Furthermore, acrA gene over-expression was significantly correlated with cross-resistance to beta-lactams including piperacillin, amoxicillin, clavulanic acid, and cefazolin. In conclusion, mutations in the QRDR are the primary mechanism for increasing fluoroquinolone resistance, and in combination with efflux pump over-expression, contribute to high-level resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • DNA Gyrase / genetics
  • DNA Topoisomerase IV / genetics
  • Drug Resistance, Bacterial / genetics*
  • Escherichia coli / drug effects
  • Escherichia coli / genetics*
  • Fluoroquinolones / pharmacology*
  • Humans
  • Membrane Transport Proteins / genetics
  • Microbial Sensitivity Tests
  • Point Mutation
  • Reverse Transcriptase Polymerase Chain Reaction


  • Anti-Bacterial Agents
  • Fluoroquinolones
  • Membrane Transport Proteins
  • DNA Topoisomerase IV
  • DNA Gyrase