This study investigates the phylogenetic relatedness of *E. coli* O157:H7 from pigs, cattle, and pork-production environments in Alberta, Canada, to determine the source of recent outbreaks linked to contaminated pork. Limited strain diversity was observed using conventional subtyping methods. Whole-genome single nucleotide polymorphism (SNP) analysis confirmed the recent ancestry of isolates from all three sources, with most environmental isolates clustering closer to pig isolates than cattle isolates. A direct link was found between 2018 outbreak environmental isolates and isolates from a pig farm in 2018. Pig isolates primarily harbored the *stx₂a* Shiga toxin gene, while cattle isolates frequently possessed both *stx₁a* and *stx₂a*. The findings suggest that pigs can be a significant source of *E. coli* O157:H7.

Peipei Zhang, Saida Essendoubi, Julia Keenliside, Tim Reuter, Kim Stanford, Robin King, Patricia Lu, Xianqin Yang