Prevalence and Characterization of Escherichia coli O157:H7 on Pork Carcasses and in Swine Colon Contents from Provincially Licensed Abattoirs in Alberta, Canada

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.

Shiga Toxin–Producing Escherichia coli (STEC) and STEC-Associated Virulence Genes in Raw Ground Pork in Canada

“…Early studies pointed out that a high rate of O157 STEC was found in ground meat (beef and pork) originating from Calgary, Alberta, Canada (25). Following three O157 STEC outbreaks in Alberta, Canada, that were associated with ground pork, a focused study was conducted in which O157 STEC was isolated from 7 (1.4%) of 504 swine colon fecal samples from healthy market swine of Albertan farms (27). Other studies have also detected O157 STEC in swine colon fecal samples obtained at slaughter facilities in the United States (32).…”

Genome Sequences of 104 Escherichia coli O157:H7 Isolates from Pigs, Cattle, and Pork Production Environments in Alberta, Canada

“…It was unclear whether the E. coli O157 isolates in the pork products were pig-adapted strains or due to cross-contamination from cattle. A surveillance study (23) and outbreak-related investigations recovered Shiga toxin gene-containing O157:H7 from pig fecal samples and pork production environments in Alberta. This study sequenced the genomes of these isolates and O157:H7 isolated from cattle in Alberta to identify the potential source of O157:H7 contaminating pork.…”

“…This study sequenced the genomes of these isolates and O157:H7 isolated from cattle in Alberta to identify the potential source of O157:H7 contaminating pork. These isolates included E. coli O157:H7 recovered from pigs (n = 41; Pig01 to Pig41), pork production-related environments (n = 25; Env01 to Env25), and cattle (n = 38; Cat01 to Cat12, Cat14 to Cat19, Cat21 to Cat23, and Cat25 to Cat41) in Alberta, Canada (23)(24)(25)(26)(27)(28)(29) (Table 1). Pig isolates were recovered from either the cecal contents of pigs in pork processing facilities or pig feces from barns (23).…”

“…These isolates included E. coli O157:H7 recovered from pigs (n = 41; Pig01 to Pig41), pork production-related environments (n = 25; Env01 to Env25), and cattle (n = 38; Cat01 to Cat12, Cat14 to Cat19, Cat21 to Cat23, and Cat25 to Cat41) in Alberta, Canada (23)(24)(25)(26)(27)(28)(29) (Table 1). Pig isolates were recovered from either the cecal contents of pigs in pork processing facilities or pig feces from barns (23). Cattle isolates were recovered from cattle rectal grabs and feces from the floors of feedlot pens or transportation trucks (24)(25)(26)(27)(28)(29).…”

“…Cattle isolates were recovered from cattle rectal grabs and feces from the floors of feedlot pens or transportation trucks (24)(25)(26)(27)(28)(29). The environmental isolates included those that had been recovered from water (Env22), manure (Env21), a mouse fecal sample (Env16), and pig feces (Env17 to Env20 and Env23 to Env25) on farms; pig carcasses (Env06 to Env14) in pork processing plants; sponge samples from processing environments (Env03 and Env15); and pork (Env01, Env02, Env04, and Env05) from retailers (23). The presence of Shiga toxin genes in these isolates was confirmed using PCR methods as described in previous studies (23)(24)(25)(26)(27)(28)(29).…”