Horizontal transfer characterization of ColV plasmids in bla_CTX-M-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_CTX-M, as the most common ESBLs subtype, in E. coli has received sustained attention around the worldwide, but the research on the pathogenicity of bla_CTX-M-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_CTX-M-positive E. coli. The multi-drug resistance traits, phylogroups, and ColV plasmid profilings were screened in 76 bla_CTX-M-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_CTX-M-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_CTX-M-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_CTX-M-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.