Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2007
Publication Date: 12/1/2007
Citation: Durso, L.M., Keen, J.E. 2007. Shiga-toxigenic Escherichia coli O157 and non-Shiga-toxigenic Escherichia coli O157 respond differently to culture and isolation from naturally contaminated bovine feces. Journal of Applied Microbiology. 103:2457-2464.
Interpretive Summary: E. coli O157 that produce Shiga-toxins are an important cause of foodborne disease in people, often due to consumption of contaminated meat or milk or from contact with infected livestock or contaminated livestock manure. Accurate detection methods are necessary to identify E. coli O157 that produce Shiga-toxins in agricultural production environments. Sensitive detection is particularly important in livestock fecal samples and in agricultural environmental samples because E coli O157 may be present in very low numbers in these sample types. In this study, we compared the performance of two recent commercially available innovations for E. coli O157 detection. We tested a large volume and a small volume recovery protocol on fecal samples from feedlot cattle that were naturally-infected with E. coli O157. The strains responded differently to the various protocols tested, depending on whether or not they had the Shiga-toxins. The large volume strategy was more sensitive than conventional small volume strategies, but also was more expensive in labor and materials. Our findings also suggest that incorporating antimicrobial selection into an E. coli O157 detection strategy helps to find the subset of E. coli O157 that potentially are more pathogenic.
Technical Abstract: We quantified the effects of two immunomagnetic separation (IMS) strategies, two broth enrichment times, and two selective plating media on isolation rates of Shiga-toxigenic Escherichia coli (STEC) O157 and non-STEC O157 from fecal specimens of naturally infected feedlot cattle. STEC O157 and non-STEC O157 strains were often isolated from the same fecal specimen and responded differently to the selection and isolation protocols. The Pathatrix**TM IMS system, which circulates a large volume (250 ml) of enrichment broth over stationary beads, was more sensitive than a conventional small volume (1 ml aliquot) IMS method at detecting STEC O157 from the naturally contaminated bovine fecal specimens. However, the Pathatrix**TM strategy was also more expensive in labor and consumable inputs. STEC O157 was more frequently isolated from 6-h enriched broth and from selective ChromAgar O157 plates containing 0.63 mg/L potassium tellurite (TCA). Non-STEC O157 was more frequently isolated from un-enriched broth and from ChromAgar O157 plates without tellurite (CA). The combination of a 6-h enrichment in Gram-negative broth containing vancomycin, cefixime and cefsuludin, large volume IMS by Pathatrix**TM, and selective plating on TCA maximized STEC O157 recovery from naturally contaminated cattle fecal specimens, but all methods evaluated resulted in the isolation of a variety of E. coli O157 subtypes. Our findings indicate that incorporating tellurite into an E. coli O157 detection strategy may select for the subset of E. coli O157 that contains the Shiga-toxin genes.