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Background
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Strains of Escherichia coli that produce Shiga-like toxins (SLTs), also known as Verocytotoxins (VTs), are an important cause of human disease. Clinical manifestations of infection include diarrhea, hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). Although Shiga-like toxin producing E. coli (SLTEC) belong to many O serogroups, serotypes O157:H7 and O157:H are the predominant SLTEC associated with HC and HUS. (Riley et al, 1983, Karmali 1989, Griffin and Tauxe 1991). Outbreaks of HC and HUS due to E. coli O157 have been linked to consumption of undercooked ground beef (Riley et al, 1983, Wells et al 1983, Padhye and Doyle, 1992). Prevalence studies indicate that up to 3.7% of retail meats may contain E. coli O157 (Doyle and Schoeni 1987). Although this may seem low compared to some other foodborne pathogens, the seriousness of disease caused by E. coli O157 has made this pathogen a major food safety concern.
Detection of E. coli O157:H7 in meats by cultural methods is time consuming, requiring several days to obtain presumptive positive results. Typically, meat samples are cultured in primary enrichment broth which is plated onto sorbitol-MacConkey (SMAC) agar. Non-sorbitol fermenting colonies are then subcultured for identification by serotyping or related methods. As some E. coli O157 strains associated with HC and HUS ferment sorbitol (Karch et al 1993), this approach may give false negative results. The Diagnostic Automation, INC. E. coli O157 ELISA is a rapid and reliable test which significantly reduces the time required to screen foods for the presence of E. coli O157. Primary enrichment cultures grown for 8-16 hours can be tested in less than one hour, allowing ELISA-negative product to be released within 24 hours. Enrichment broths presumptively positive for E. coli O157 on the basis of positive ELISA tests can be cultured further for confirmation by standard methods.
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