Purpose: This study was performed to investigate i) the prevalence of FQ resistance and plasmid mediated quinolone resistance (PMQR) genes in Escherichia coli isolated from swine, and ii) the antimicrobial resistance profile and FQ resistance mechanisms of FQ resistant E. coli.
Methods: Escherichia coli were isolated from 237 swine feces. FQ resistant E. coli were identified by the standard disk diffusion test and PMQR were detected by PCR. Antimicrobial susceptibility tests were performed against 16 different antimicrobial agents, and the 3 major FQ resistance mechanisms were investigated by sequencing of quinolone resistance determining regions (QRDR), detection of PMQR, and measuring of efflux pump activity.
Results: Of 171 E. coli isolates, 59 (34.5%) isolates were determined as FQ-resistant. Of 59 FQ-resistant isolates, PMQR genes were detected in nine isolates (15.3%). Efflux pump activity was found in 56 isolates (94.9%). Point mutation in QRDR was detected in all 59 isolates (100%) and determined to be the main cause of FQ resistance. Of 59 FQ-resistant E. coli, 54 isolates (91.5%) were classified as multi-drug resistant E. coli and 11 isolates (18.6%) were confirmed as extended-spectrum beta-lactamase producing E. coli.
Significance: Although the use of FQ as a feed additives has been prohibited in Korea, the prevalence of FQ resistance and PMQR genes has increased considerably in swine. The increased FQ resistance may be, in part, due to the increased use of FQ for self-treatment and therapeutic purposes. Therefore, prudent use of FQ in animal farms is warranted to reduce the evolution of FQ-resistant bacteria in the animal industry.