Rapid Increase in the IS 26 -Mediated cfr Gene in E. coli Isolates with IncP and IncX4 Plasmids and Co-Existing cfr and mcr-1 Genes in a Swine Farm

This paper aimed to investigate the molecular epidemiological features of the gene in isolates in a typical swine farm during 2014-2017. A total of 617 isolates were screened for the gene using PCR amplification. A susceptibility test, pulsed-field gel electrophoresis (PFGE), S1-PFGE, southern blotting hybridization, and the genetic context of the gene were all used for analyzing all -positive isolates. A conjugation experiment was conducted with the broth mating method using C600 as the recipient strain and 45 -bearing isolates as the donor strain. Plasmids pHNEP124 and pHNEP129 were revealed by Illumina Miseq 2500. Eighty-five (13.7%) isolates were positive for the gene and the prevalence of the gene had significantly increased from 1.6% in 2014 to 29.1% in 2017. The Pulsed-Field Gel Electrophoresis (PFGE) analysis indicated that the spread of the gene among isolates was mainly due to horizontal transfer. In addition, the gene was primarily located on the plasmids between 28.8-kb to 60-kb in size, and the gene was flanked by two copies of IS with the same orientation. Sequence analysis suggested that the plasmids pHNEP124 and pHNEP129 co-harboring the and genes belonged to the plasmids IncP plasmid and IncX4 plasmid, respectively. In conclusion, this is the first study to report the high prevalence of the gene among isolates and the first report of the complete genome sequence of IncP and IncX4 plasmids carrying the and genes. The occurrence and dissemination of the -carrying plasmids among isolates need further surveillance.