Abstract
Three E. coli O157:H7 outbreaks have been attributed to contaminated pork in Alberta, Canada, recently. This study investigates the phylogenetic relatedness of E. coli O157:H7 from pigs, cattle, and pork-production environments for source attribution. Limited strain diversity was observed using five conventional subtyping methods, with most or all strains being in one subgroup. Whole-genome single nucleotide polymorphism analysis confirmed the recent ancestry of the isolates from all three sources. Most environmental isolates clustered closer with pig isolates than cattle isolates. Also, a direct link was observed between 2018-outbreak environmental isolates and isolates collected from a pig farm in 2018. The majority of pig isolates harbor only one Shiga toxin gene, stx2a, while 70% (35/50) of the cattle isolates have both stx1a and stx2a. The results show some E. coli O157:H7 strains could establish persistence on pig farms and as such, pigs can be a significant source of the organism.
Highlights
Shiga toxin-producing Escherichia coli (STEC) can cause human enteric illness ranging from uncomplicated diarrhea to bloody diarrhea, with a fraction (2–22%) of patients developing lifethreatening hemolytic uremic syndrome (HUS)[1,2,3,4,5,6]
The predominant STEC serotype associated with human infections and outbreaks in North America is O157:H7/NM, which has a higher association with severe patient outcomes, compared to other serotypes[1,7]
Outbreaks attributed to STEC O157:H7 contaminated pork products are scarce worldwide[11]; a higher frequency has been observed in Alberta, Canada, with three outbreaks having occurred in four years (2014, 2016, and 2018)[12,13,14]
Summary
Shiga toxin-producing Escherichia coli (STEC) can cause human enteric illness ranging from uncomplicated diarrhea to bloody diarrhea, with a fraction (2–22%) of patients developing lifethreatening hemolytic uremic syndrome (HUS)[1,2,3,4,5,6]. A large number of studies from various geographical regions have been conducted to investigate the prevalence of STEC O157: H7 in healthy pigs[15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33] Most of these studies did not find this pathogen in pigs[16,17,18,19,20,22,25,26,27,31,33], except for the studies from Japan[32], Ireland[23], UK24, Sweden[28], Norway[30], USA29, and Canada[15] where up to 2% prevalence was reported. In the present study, we analyzed the population structure and phylogenetic relatedness of 121 STEC O157:H7 isolates from pigs (n = 41), cattle (n = 51), and pork-production environments (n = 30) in Alberta, Canada using both conventional and WGS-based subtyping methods. The genomes of these isolates were characterized with a focus on virulence and antibiotic resistance genes
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