Characterization of fluoroquinolone resistance mechanisms and their correlation with the degree of resistance to clinically used fluoroquinolones among Escherichia coli isolates.
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.
Chang
Tsung-Ming
TM
Department of Microbiology, Faculty of Medicine (Graduate Institute of Medicine), College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
Lu
Po-Liang
PL
Li
Hsuan-Hui
HH
Chang
Chung-Yu
CY
Chen
Tun-Chieh
TC
Chang
Lin-Li
LL
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics; D008826:Microbial Sensitivity Tests; D017354:Point Mutation; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase