Abstract

The fluoroquinolone resistance mechanism of four laboratory developed fluorquinolone resistant strains of Escherichia coli was studied. Fluoroquinolone concentrations inside the resistant cells were similar to the concentrations in the susceptible cells. DNA sequencing of the quinolone resistance determining regions (QRDR) in gyrA and parC revealed the presence of Ser 83Leu and Asp87Gly mutations in GyrA, and Gly78Cys and Ser80Arh mutations in ParC of the ofloxacin, norfloxacin, and HK3140 resistant strains, while the ciprofloxacin resistant strain had Ser83Leu and Aasp87Tyr mutations in GyrA, and Gly78Cys and Ser80Ile mutations in ParC. A Gly78Cys substitution in ParC was newly detected in this work and seemed to be responsible for the extremely high MICs to fluroquinolones.

• Keywords: Fluoroquinolone; resistance mechanism; parC; gyrA; Escherichia coli; DNA gyrase; topoisomerase IV