Genetic diversity of extended-spectrum cephalosporin resistance in Salmonella enterica and E. coli isolates in a single broiler chicken.

Extended-spectrum cephalosporin (ESC) resistance investigated in Salmonella and E. coli from the same chicken was to improve the understanding of the inter-species transmission of ESC resistance determinants in Salmonella and E. coli from a single chicken individual. Fifteen (13.6%) farms and 44 (8.0%) chicken individuals were positive for ESC-resistant E. coli and/or Salmonella, 8 farms (7.3%) and 12 (2.2%) individuals were simultaneously positive for ESC-resistant E. coli and Salmonella. The genetic diversity of ESC resistance determinants in E. coli and Salmonella was observed. Most E. coli isolates (67.6%) produced CTX-M-type of blaCTX-M-55, and 9 isolates (24.3%) produced CMY-type of blaCMY-2. Most Salmonella isolates (94.1%) produced blaCTX-M-15. Two broiler chicken farms were simultaneously positive for blaCMY-2- and blaCTX-M-15-harboring E. coli and Salmonella isolates. Whole-plasmid sequence for the transferable plasmid harboring blaCMY-2 showed genomic diversity of the plasmids from Salmonella and E. coli sourced from the same chicken. The genetic arrangement of blaCMY-2 in Salmonella was IS1294b-ΔISEcp1-blaCMY-2-blc-sugE and ISEcp1-blaCMY-2-blc-sugE in E. coli located on multi-host plasmids of IncI1-pST-2 and IncI1-pST-12. In conclusion, the study illustrates the genetic diversity of ESC resistance determinants in E. coli and Salmonella in a single chicken. Considering the possibility of transmission of antimicrobial resistance to humans through the food chain, a large reservoir of ESC resistance in chicken which could be co-infected with ESC-resistant E. coli and Salmonella poses a serious risk of potential transmission of ESC-resistant E. coli and Salmonella, and their transferable ESC resistant gene, to human simultaneously.