Fluoroquinolone antimicrobial resistance of Escherichia coli isolated from swine feces in Korea

Abstract

In this study, the fluoroquinolone (FQ) resistance rate and mechanisms in FQ-resistant Escherichia coli isolated from swine fecal samples have been investigated. A total of 171 E. coli isolates were collected from 237 swine fecal samples (72.2%). Of these, 59 isolates (34.5%) were confirmed as FQ-resistant E. coli by the disk diffusion method. Of the FQ-resistant isolates, three major FQ-resistance mechanisms were investigated: i) amino acid substitutions in quinolone resistance-determining regions (QRDRs), ii) acquisition of plasmid-mediated quinolone-resistance genes (PMQRs

qnrA, qnrB, qnrS, qepA, and aac(6)-Ib-cr), and iii) increased efflux pump activity. All 59 ciprofloxacin (CIP)-resistant isolates had gyrA mutations (100%)

of these 59 isolates, 58 had mutations in parC (98.3%), 22 had mutations in parE (37.3%), and none had mutations in gyrB. The predominant mutation was Ser83Leu in gyrA, followed by Ser80Ile in parC, and Ser458Ala in parE. Nine isolates harbored PMQR genes, including qnrS (n = 7, 11.9%), qepA (n = 1, 1.7%), and aac(6)-Ib-cr (n = 1, 1.7%). Efflux pump activity was found in 56 isolates (94.9%). FQ-resistant E. coli had high minimum inhibitory concentrations against CIP, and most isolates were multidrug-resistant. Compared with previous studies in Korea, the prevalence of FQ resistance and PMQR genes had increased significantly in swine. Although the use of FQ as a feed additives is prohibited in Korea, use for self-treatment and therapeutic purposes has been increasing, which may be responsible for the higher FQ-resistance rate observed in this study. Therefore, prudent use of FQ in animal farms is needed to reduce the evolution of FQ-resistant bacteria in Korea.