Co-carriage of qnrS1, floR, and bla(CTX-M-14) on a multidrug-resistant plasmid in Escherichia coli isolated from pigs.

Plasmid-mediated quinolone resistance (PMQR) determinants were widely distributed among Enterobacteriaceae. The objectives of the present study were to analyze PMQR-positive Escherichia coli isolates from pigs, and to investigate the association between these determinants and other resistant genes. A total of 129 porcine E. coli isolates were included in this study. The presence of PMQR, floR, bla(CTX-M-14), and bla(TEM-1) genes were detected by polymerase chain reaction (PCR) amplification and confirmed by subsequent sequencing. The PMQR-positive isolates were subjected to plasmid profiling, and transformation experiments were conducted to identify the quinolone resistance plasmids. The qnrS1 region of a quinolone resistance plasmid was cloned and sequenced. Among the 129 E. coli isolates, the positive rate for PMQR determinants was 42.6%, and the prevalence of qnr genes, aa(6')-Ib-cr, and qepA were 23.3%, 18.6%, and 0.8%, respectively. A qnrS1-carrying plasmid of 81 kb, named plasmid T078 (pT078), was detected from one multidrug-resistant isolate. Hybridization and PCR analysis confirmed that floR, bla(CTX-M-14), and bla(TEM-1) genes were also located on this plasmid. Sequence analysis identified the qnrS1 gene flanked by a truncated transposase gene. Moreover, complete tetracycline resistance genes tet(A) and tet(R) were found upstream of the qnrS1 gene, and floR gene was found downstream of the qnrS1 gene on the plasmid pT078. To our knowledge, this is the first study demonstrating the occurrence of qnrS1, floR, bla(CTX-M-14), bla(TEM-1), and tet(A) on one plasmid in E. coli isolated from food animals.