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 bla, and 9 isolates (24.3%) produced CMY-type of bla. Most Salmonella isolates (94.1%) produced bla. Two broiler chicken farms were simultaneously positive for bla- and bla-harboring E. coli and Salmonella isolates. Whole-plasmid sequence for the transferable plasmid harboring bla showed genomic diversity of the plasmids from Salmonella and E. coli sourced from the same chicken. The genetic arrangement of bla in Salmonella was IS1294b-ΔISEcp1-bla-blc-sugE and ISEcp1-bla-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.