Abstract
Often Escherichia coli are harmless and/or beneficial bacteria inhabiting the gastrointestinal tract of livestock and humans. However, Shiga toxin-producing E. coli (STEC) have been linked to human disease. Cattle are the primary reservoir for STEC and STEC “super-shedders” are considered to be a major contributor in animal to animal transmission. Among STEC, O157:H7 is the most recognized serotype, but in recent years, non-O157 STEC have been increasingly linked to human disease. In Argentina and Germany, O178 is considered an emerging pathogen. Our objective was to compare populations of E. coli O178, O157, shiga toxin 1 and 2 in western Canadian cattle feces from a sampling pool of ~80,000 beef cattle collected at two slaughterhouses. Conventional PCR was utilized to screen 1,773 samples for presence/absence of E. coli O178. A subset of samples (n = 168) was enumerated using droplet digital PCR (ddPCR) and proportions of O178, O157 and shiga toxins 1 & 2 specific-fragments were calculated as a proportion of generic E. coli (GEC) specific-fragments. Distribution of stx1 and stx2 was determined by comparing stx1, stx2 and O157 enumerations. Conventional PCR detected the presence of O178 in 873 of 1,773 samples and ddPCR found the average proportion of O178, O157, stx1 and stx2 in the samples 2.8%, 0.6%, 1.4% and 0.5%, respectively. Quantification of stx1 and stx2 revealed more virulence genes than could be exclusively attributed to O157. Our results confirmed the presence of E. coli O178 in western Canadian cattle and ddPCR revealed O178 as a greater proportion of GEC than was O157. Our results suggests: I) O178 may be an emerging subgroup in Canada and II) monitoring virulence genes may be a more relevant target for food-safety STEC surveillance compared to current serogroup screening.
Highlights
Escherichia coli are commensal organisms found in the gastrointestinal tract of both humans and livestock and a subgroup has been linked to human diseases
O178 was identified across all seasons at both sampling sites in Alberta (Table 2) and differed in seasonal prevalence (P = 0.0001) with O178 presence higher in winter compared to summer
The O178 amplicons were on average 1.5-times higher at site A compared to B (P < 0.05), which is inconsistent with the findings of the conventional O178 PCR screening (Table 2)
Summary
Escherichia coli are commensal organisms found in the gastrointestinal tract of both humans and livestock and a subgroup has been linked to human diseases. Certain pathogenic E. coli cause extra intestinal illnesses (e.g. urinary tract infections) and various other groups such as Shiga toxin-producing E. coli (STEC) may cause gastrointestinal diseases [1]. All STEC produce at least one Shiga toxin [2] and can cause illness ranging from mild diarrhea to severe infections such as hemolytic uremic syndrome or hemorrhagic colitis [3, 4], and have been linked to both outbreaks and sporadic cases of disease [5]. Cattle are a major reservoir for STEC [6] and are often implicated as the origin of entry into the food chain [7]. A Scottish study found that 9% cattle were “super-shedders” but accounted for >96% of the E. coli O157 shed by the group [10]. Super-shedding is not limited to O157 as STEC O26 “super-shedders” have been identified in the past [8]
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