Abstract
This study was aimed to determine the resistance rate of fluoroquinolones for 112 Escherichia coli isolates from Prince Salman Hospital, Riyadh and to detect the mutations in the quinolone resistance-determining region (QRDR) of gyrA and parC in the fluoroquinolones resistant isolates. The resistance rate of ciprofloxacin for E. coli isolates was 37.5%. Amplification and determination of the QRDR of the gyrA and parC genes were done in four selected E. coli isolates with different importance of minimum inhibitory concentration (MIC) values ranging from 2 to 64 mg/L. A single mutation in gyrA (Ser TCG-83 -> Leu TTG) was detected in the isolate with a reduced susceptibility to ciprofloxacin (MIC 2 mg/L). Three mutations were detected in E. coli isolates with ciprofloxacin MIC >= 16 mg/L. Double mutations in gyrA (Ser-83 -> Leu and Asp-87 -> Asn) and a single mutation in parC (Ser-80 -> Ile). This study demonstrates that the alterations in gyrA and parC subunits have significant role in conferring quinolone resistance in clinical isolates form Saudi Arabia.