Fluoroquinolone resistance and gyrA and parC mutations of Escherichia coli isolated from chicken

Escherichia coli is a common inhabitant of the intestinal tracts of animals and humans. The intestines of animals also represent an ideal environment for the selection and transfer of antimicrobial resistance genes. The aim of this study was to investigate the resistance of E. coli isolated from chicken fecal samples to fluoroquinolones and to analyze the characterization of mutations in its gyrA and parC gene related resistance. One hundred and twenty-eight E. coil isolates showed a high resistance to ciprofloxacin (CIP; 60.2%), enrofloxacin (ENO; 73.4%) and norfloxacin (NOR; 60.2%). Missense mutation in gyrA was only found in the amino acid codons of Ser-83 or Asp-87. A high percentage of isolates (60.2%) showed mutations at both amino acid codons. Missense mutation in parC was found in the amino acid codon of Ser-80 or Glu-84, and seven isolates showed mutations at both amino acid codons. Isolates with a single mutation in gyrA showed minimal inhibitory concentrations (MIC) for CIP (≤0.5 to 0.75 μg/ml), ENO (1 to 4 μg/ml) and NOR (0.75 to 4 μg/ml). These MIC were level compared to isolates with two mutations, one in gyrA and one in parC, and three mutations, one in gyrA and two in parC (CIP, ≤0.5 to 3 μg/ml; ENO, 2 to 32< μg/ml; NOR, 1.5 to 6 μg/ml). However, the isolates with two mutation in gyrA regardless of whether there was a mutation in parC showed high MIC for the three fluoroquinolones (CIP, 0.75 to 32≤μg/ml; ENO, 3 to 32≤μg/ml; NOR, 3 to 32≤μg/ml). Interestingly, although the E. coil used in this study was isolated from normal flora of chicken, not clinical specimens, a high percentage of isolates showed resistance to fluoroquinolones and possessed mutations at gyrA and parC associated with fluoroquinolone resistance.