Genomic characterization of pathotype diversity and drug resistance among generic Escherichia coli isolated from broiler chickens in Canada.

Escherichia coli is a Gram-negative bacterium that is ubiquitous in animals and humans, with some strains capable of causing disease. The aim of this study was to perform a comparative genomic analysis of 2732 generic E. coli isolates that were recovered from poultry samples collected from six regions in Canada as part of the National Microbiological Baseline study in Broiler Chicken. Isolates were subjected to whole genome sequencing and a subset (1122/2732) were tested for phenotypic resistance to 15 antimicrobials. These E. coli isolates were highly diverse, representing 376 serotypes, 236 sequence types and 21 pathotypes, of which 19 were hybrid pathotypes. A high concordance (>85%) between resistance phenotype and the presence of antimicrobial resistance genes and point mutations (resistance determinants) was observed for 13/15 antimicrobials. Over 95% of the β-lactam, fluoroquinolone, and phenicol resistance genes were predicted to be plasmid-borne. The number of resistance determinants per genome was highest in Quebec, while resistance genes associated with β-lactam resistance were more frequently detected in isolates from British Columbia. Generic E. coli in Canadian poultry are highly diverse, can carry pathotype-associated virulence factors and resistance determinants of clinical significance with a risk of emerging into pathogenic strains.