Horizontal transfer characterization of ColV plasmids in bla-bearing avian Escherichia coli.

Extended-spectrum-β-lactamases (ESBLs)-producing Escherichia coli conferred resistance to most β-lactams, except for carbapenems. To date, the transmission mechanism of bla, as the most common ESBLs subtype, in E. coli has received sustained attention around the worldwide, but the research on the pathogenicity of bla-bearing E. coli is still scarce. The aims of this study were to discern the spread characteristics of ColV (encoding colicin V) plasmids in bla-positive E. coli. The multi-drug resistance traits, phylogroups, and ColV plasmid profilings were screened in 76 bla-positive E. coli. Thereafter, the genetic profiles of E. coli G12 and GZM7 were determined by whole genome sequencing, conjugation and S1-pulsed-field gel electrophoresis. The median lethal dose was analyzed in E. coli G12 and TG12A, the ColV-plasmid transconjugant of G12. Of all 76 bla-bearing E. coli, 67.11% exhibited resistance to at least 2 drugs in addition to ceftiofur, 14.47% carried ColV-positive plasmids, and 53.95% were phylogroup C. Further studies demonstrated that the bla-bearing E. coli G12 was assigned to the predominant lineage O78:H4-ST117 of phylogroup G. In addition, its ColV-positive plasmid simultaneously carried multiple resistance genes, and could be independently transferred to confer partial pathogenicity on its host by plasmid mating. E. coli GZM7 was O53:H9-ST23 of phylogroup C, which belonged to another representative lineage of APEC (avian pathogenic E. coli). Its ColV-positive plasmid could complete conjugation with the help of the other coexisting-resistance conjugative plasmid, although it failed to transfer alone. Our findings highlight the flexibly horizontal transfer of ColV plasmids along with multidrug-resistant genes among bla-bearing E. coli poses a threat to poultry health and food safety, which contributes to elucidate the concept of "One Health" and deserves particular concern.