Dissemination of Escherichia coli carrying plasmid-mediated quinolone resistance (PMQR) genes from swine farms to surroundings.

Different samples were collected from three swine farms in China to investigate the spread of antibiotic-resistant Escherichia coli. A total of 130 E. coli isolates were obtained from feces, air, river water, silt, and soil samples and characterized. The susceptibility of the E. coli isolates to 19 antibiotics was tested. The results revealed that the resistance rates of the E. coli isolates against 9 antibiotics were high. The minimum inhibitory concentration (MIC) values of ciprofloxacin, ofloxacin, and nalidixic acid were mainly in the ranges of 2-64, 8-64, and 8-64 μg/ml. The plasmid-mediated quinolone resistance (PMQR) genes qnr, aac(6')-Ib-cr, qepA, and oqxAB were detected by polymerase chain reaction (PCR), and the similarity of E. coli from different samples was identified by pulsed-field gel electrophoresis (PFGE). The detection rates of the qnrA, qnrB, qnrS, aac(6')-Ib-cr, qepA, and oqxAB genes in the E. coli isolates from three swine farms were in the range of 10.87-23.08%, 13.04-20.51%, 40.00-43.48%, 30.43-38.46%, 6.52-12.82%, and 7.69-17.39%, respectively. The PFGE result showed that 49% (49/100) of isolates originating from air, river water, soil, and silt samples had ≥85% similarity to fecal-obtained isolates, and 40.82% (20/49) of them shared the same PMQR genes with fecal-obtained isolates. This indicated that E. coli carrying PMQR genes and originating from feces in swine farms could spread to the external environment, which could be a potential threat to the public environment and human health.