Plasmid and chromosomal copies of blaCMY-2 mediate resistance to third-generation cephalosporins in Escherichia coli from food animals in China.

ABSTRACT

The use of antimicrobials in food animals is the major determinant for the propagation of resistant bacteria in the animal reservoir. The objective of this study was to investigate the presence and distribution of third-generation cephalosporin (3GC) -resistant and plasmid-mediated AmpC (pAmpC)-producing Escherichia coli isolated from food animals in Southern China. In total, 744 3GC-resistant and 40 blaCMY-2-positive E. coli strains were recovered from 1656 food animal fecal samples across five rearing regions. The blaCMY-2 genes were located on IncC, IncFIB or IncI1 type plasmids in 12 E. coli isolates. In the other 22 isolates, S1-PFGE and hybridization analyses revealed that the blaCMY-2 gene was chromosomally located and demonstrated a high prevalence of the chromosomally encoded blaCMY-2 gene in E. coli. Plasmid stability and growth curve experiments demonstrated that IncI1, IncC and IncFIB plasmids can exist stably in the host bacteria and with a low growth burden and may be the reason these plasmids can be widely disseminated in breeding environments. Whole genome sequencing indicated that ISEcp1 and IS1294 played important roles in blaCMY-2 transfer to both plasmids and the chromosome. Our study confirmed that blaCMY-2 mediated resistance of food animal-derived E. coli to 3GC and highlights the urgent need for appropriate monitoring programmes.