Outer Membrane Vesicles of Avian Pathogenic Escherichia coli Mediate the Horizontal Transmission of bla(CTX-M-55)

The CTX-M-55 type extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae is increasing in prevalence worldwide without the transmission mechanism being fully clarified, which threatens public and livestock health. Outer membrane vesicles (OMVs) have been shown to mediate the gene horizontal transmission in some species. However, whether bla(CTX-M-55) can be transmitted horizontally through OMVs in avian pathogenic Escherichia coli (APEC) has not been reported yet. To test this hypothesis, an ESBL-producing APEC was isolated and whole-genome sequencing (WGS) was performed to analyze the location of bla(CTX-M-55). Ultracentrifugation and size exclusion chromatography was used to isolate and purify OMVs, and the transfer experiment of bla(CTX-M-55) via OMVs was performed finally. Our results showed that the bla(CTX-M-55) was located on an IncI2 plasmid. The number and diameter of OMVs secreted by ESBL-producing APEC treated with different antibiotics were significantly varied. The transfer experiment showed that the OMVs could mediate the horizontal transfer of bla(CTX-M-55), and the frequency of gene transfer ranged from 10(−5) to 10(−6) CFU/mL with the highest frequency observed in the Enrofloxacin treatment group. These findings contribute to a better understanding of the antibiotics in promoting and disseminating resistance in the poultry industry and support the restrictions on the use of antibiotics in the poultry industry.