Abstract
Since the use of fluoroquinolone antibiotic in clinical practice was introduced about two decades ago, quinolone-resistant E. coli strains are being isolated with increasing frequency. This study devotes 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%. We have determined QRDR of the gyrA and parC genes of ciprofloxacin resistant E. coli (MIC 2-64 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 suggests, that in clinical isolates of E. coli, DNA gyrase is a primary target of quinolones, that only a single amino acid change at Ser-83 in GyrA is sufficient to generate high-level resistance to nalidixic acid and to decrease susceptibility to ciprofloxacin, and that the accumulation of amino acid changes in GyrA and the simultaneous presence of the ParC alterations play a central role in developing high-level resistance to ciprofloxacin.Key words: Fluoroquinolones resistance, gyrA, parC, Saudi Arabia.