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Zoonotic pathogens, like Shiga toxin-producing Escherichia coli (STEC) are a food safety and health risk. Among STEC, O157 is considered a major pathogen; however, globally the number of outbreaks with new emerging STEC strains is rising. Here, quantitative data on STEC O157 were gathered for western-Canada beef cattle and compared to emerging STEC. Quantitative data revealed; O178 is 4-times more numerous than O157 and high Shiga-toxin events are often not attributed to O157. Results suggest current surveillance likely misses emerging STEC due to restricted O-serogroup screening. Secondly, an alternate STEC mitigation strategy was investigated as an alternative approach to use of antibiotics which is controversial in human and animal therapeutics. Competition experiments identified a strong E. coli O103F which incapacitated STEC growth by producing a diffusible antimicrobial, most likely a microcin. The antimicrobial revealed tremendous potential for use along the farm-to-fork continuum or in human intervention to mitigate STEC.

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.

Escherichia coli O157:H7 is an enteric pathogen that can cause severe gastrointestinal disease, sometimes leading to hospitalization and death. These bacteria have a variety of virulence factors that can be encoded for on pathogenicity islands (PAIs). The goal of this study was to characterize specific E. coli O157:H7 PAI deletion mutants using three methods: Phentotype Microarrays (PM), growth curves and survival curves were used to elucidate possible roles for the PAIs. Results from the PM study suggest that PAIs have a role in carbon substrate utilization; i.e., four of the O-island (OI) deletion mutants (OI-87, 98, 102 and 172) and an S-Loop (SL-72) deletion mutant exhibited differences in substrate utilization (gains and losses in utilization) compared to parental O157:H7 strains EDL933 (OI) and Sakai (SL), respectively. All of the mutants with the exception of the OI-135 mutant exhibited differences in level of substrate utilization for substrates shown to have important roles in the bacterium. Cell growth results showed that three OI deletion mutants (OI-55, 87 and 102) and the SL (SL-72) mutant exhibited a difference in rate of growth compared to the parental strains. Cell viability results showed that seven of the OI deletion mutants (OI-51, 55, 98, 108, 135, 172 and 176) exhibited different rates of decline in cell number when transferred to sterile water compared to the parental strain. The results show that removal of PAIs from E. coli O157:H7 can affect carbon utilization, growth and survival demonstrating the importance of PAIs in the ecology of these bacteria.