EFFECTS OF SRP VACCINATION ON THE PREVALENCE AND LOAD OF E. COLI O157:H7 AND NON-O157 STEC ON THE HIDES OF BEEF CATTLE AT HARVEST

Escherichia coli O157:H7 remains the major foodborne pathogen of concern for the beef industry. Extensive research has been conducted and is on-going to identify and develop novel pre- and post-harvest intervention strategies to reduce E. coli O157:H7 from live cattle and processed carcasses. Recent work has shown that hides are the main source of beef carcass contamination at slaughter and as such reductions in the prevalence of E. coli O157:H7 on the hide are directly correlated to lower carcass prevalence rates. While post-harvest interventions have been designed that address hide contamination directly, the aim of preharvest intervention is to reduce hide contamination indirectly through lowering the prevalence and levels of E. coli O157:H7 shed in the feces of cattle. Emerging technologies to reduce the prevalence of E. coli O157:H7 from cattle before arrival at a harvest facility have proven promising in small scale feedlot studies. ARS Scientists showed the Epitopix vaccine product, a SRP based E. coli O157:H7 vaccine, reduced fecal prevalence by 85% and enumeration in the positive samples by 98% in a small field trial. The present study will evaluate the efficacy of the Epitopix SRP E. coli O157:H7 vaccine under large scale commercial conditions. The vaccinated cattle will be compared to cattle slaughter during the same timeframe from feedlots in the same general region. While E. coli O157:H7 is the main target of the vaccine and the focus of this proposal, we will also analyze a subset of samples for vaccine effects on non-O157 Shiga toxin-producing E. coli (STEC). Added Project Objective: Determine relatedness of E. coli O157:H7 isolates obtained from hide and fecal samples. In evaluating the effect of the SRP vaccine in reducing E. coli O157 prevalence associated with feedlot cattle and, subsequently, in beef trim, the prevalence of E. coli O157:H7 in hide samples did not follow the same trends seen for fecal samples and in beef trim. Our belief is that this was caused by increases in hide contamination usually seen in the lairage environments at beef processing plants. Five hundred E. coli O157:H7 isolates collected from hide and fecal samples will be analyzed by PFGE. E. coli O157:H7 isolate fingerprints generated and analyzed in this study will be based on PFGE separation of Spel-digested genomic DNA. The data collected will provide clarity in determining the efficacy of the SRP vaccine.