Prevalence of plasmid-mediated quinolone resistance in Escherichia coli isolated from diseased animals in Taiwan

Escherichia coli (E. coli) is a zoonotic pathogen that often causes diarrhea, respiratory diseases or septicemia in animals. Fluoroquinolones are antimicrobial agents used to treat pathogenic E. coli infections. In this study, 1,221 E. coli strains were isolated between March, 2011 and February, 2014. The results of the antimicrobial susceptibility testing showed a high prevalence of quinolone resistance. The antimicrobial resistance rates of these E. coli isolates to nalidixic acid (NAL) were 72.0% in swine, 81.9% in chickens, 81.0% in turkeys, 64.0% in ducks and 73.2% in geese. Among these isolates, the positive rate for the plasmid-mediated quinolone resistance (PMQR) determinant was 14.8% (181/1,221); the detection rate for qnrS1 was the highest (10.2%), followed by aac(6')-Ib-cr (4.5%) and qnrB2 (0.3%). The quinolone-resistance determining regions (QRDRs) analysis for the PMQR-positive isolates showed that the strains with mutations at codon 83 or 87 in GyrA were resistant to NAL. To the best of our knowledge, this is the first report of occurrence of qnrB2, qnrS1 and aac(6')-Ib-cr genes and high frequency (56.4%; 102/181) of mutation in gyrA or parC among PMQR-positive E. coli strains derived from diseased animals in Taiwan.