Dissemination of IncFII plasmids carrying rmtB and qepA in Escherichia coli from pigs, farm workers and the environment

Fifty-one fluoroquinolone-resistant Escherichia coli isolates recovered from pigs, workers and environmental samples in one pig farm were screened for 16S rRNA methylase genes and qepA, a fluoroquinolone efflux pump gene, by PCR. Clonal relatedness of the E. coli isolates was examined by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing and phylogenetic analysis. Plasmids from the E. coli isolates were characterized by incompatibility group, restriction enzyme digestion and Southern hybridization analysis. The genetic environment of rmtB and qepA was also determined by PCR mapping. Eleven isolates that were highly resistant to amikacin and fluoroquinolones were positive for rmtB and qepA.  All of these isolates belonged to phylogenetic group A, but most of them had different PFGE patterns or belonged to different sequence types (STs). Four isolates from different sources (two from pigs, one from a farm worker and one from an environmental sample) belonged to the same ST (ST160). Both rmtB and qepA were located on approximately 75-kb IncFII conjugative plasmids with nearly the same EcoRI digestion pattern. Tn3, IS26 and ISCR3 were found to be associated with rmtB and qepA. This study has found, for the first time, the transmission of rmtB and qepA among E. coli isolates from pigs, farm workers and the environment. Both horizontal transfer of IncFII plasmids and clonal dissemination have occurred and been seen to contribute to the dissemination of these resistance genes in a pig farm.