Mutations in the quinolone resistance-determining regions associated with ciprofloxacin resistance in Pseudomonas aeruginosa isolates from Southern Taiwan

Mutations in the quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC, and parE have been characterized among the 232 isolates of ciprofloxacin (CIP)-resistant Pseudomonas aeruginosa. As expected, no mutations in the QRDRs of four target genes were detected in the CIP-susceptible isolates of P. aeruginosa. It was noted that P. aeruginosa showing no mutation in the QRDRs of target genes were frequently found in isolates with a CIP in minimal inhibitory concentration (MIC) = 2 μg/mL than those of isolates with a CIP in MIC ≥4 μg/mL. The prevalence of P. aeruginosa with no mutations in the QRDRs of target genes is higher in isolates only resistant to CIP than in isolates resistant to CIP and other drugs. Double mutations occurring in gyrA and parC genes associated with a high-level resistance to CIP in MICs ≥4 μg/mL were found in 101 out of 176 isolates. Furthermore, mutations in parC and parE joined with mutation in gyrA were commonly found in P. aeruginosa highly resistant to CIP.