ABSTRACT The objective of this study was to determine the prevalence of Shiga toxin-producing E. coli (STEC) O157:H7 in colon content and on carcasses from pigs slaughtered at provincially licensed abattoirs (PLAs) in Alberta. In 2017, carcass sponge samples and colon content samples were collected from 504 healthy market hogs at thirty-nine PLAs and analyzed for E. coli O157:H7. Carcass samples were also analyzed for generic E. coli and aerobic colony count (ACC). Of the 504 carcass samples, nine were confirmed positive for E. coli O157:H7 (1.8%). Of the 504 colon content samples, seven were confirmed positive for E. coli O157:H7 (1.4%). These positives were found in 12.8% (5/39) of the PLAs, from hogs originating from eight farms. The E. coli O157:H7 isolates recovered from the positive samples (n=1 isolate per sample) were clonal, as determined by pulsed-field gel electrophoresis (PFGE). Six E. coli O157:H7 isolates obtained over a period of eight months from one PLA that only processed hogs and sourced hogs from one farm had indistinguishable PFGE patterns. All these 16 E. coli O157:H7 isolates harbored eae and ehxA , and were of stx 2a subtype, suggesting that swine can carry E. coli O157:H7 of importance to human health. All carcass sponge swabs (100%) were positive for ACC. Generic E. coli were present in 72% of carcass swabs. Carcasses from PLAs slaughtering both beef and hogs had a numerically higher ACC mean value but not statistically different compared to the PLAs slaughtering only swine (2,799 cfu/cm 2 and 610 cfu/cm 2 respectively). Generic E. coli showed a similar trend with a mean value of 0.88 cfu/cm 2 in PLAs slaughtering both species and 0.26 cfu/cm 2 in PLAs slaughtering only swine (P ≤ 0.05). This study provides evidence that healthy market hogs from different producers/farms in Alberta can carry E. coli O157:H7 and some strains of the organism may be able to establish persistence on some swine farms.

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