The research will focus on prevalence, ecology and on-farm interventions of Shiga-toxin-producing Escherichia coli and Salmonella and prevalence, amplification and dissemination of antimicrobial resistance in cattle and swine. The specific objectives are: <OL> <LI> Develop and improve methods to detect and characterize E. coli O157 and Salmonella serotypes in cattle and swine. <LI> Study the prevalence and factors affecting gut persistence and fecal shedding of E. coli O157 and Salmonella serotypes. <LI> Identify management strategies and production practices that might be manipulated to reduce fecal shedding. <LI> Study the ecology (prevalence, amplification, and dissemination) of antimicrobial resistance in fecal bacteria in cattle and swine.
NON-TECHNICAL SUMMARY: The food supply in the US is one of the safest in the world; however, foodborne illnesses do occur and frequently are associated with foods derived from animal agriculture. The livestock and meat industries have continuously sought improvements in the safety of their products and have demanded efforts to eliminate or reduce pathogen load, focusing on both pre- and post-harvest intervention strategies. The two foodborne pathogens of interest are Shiga-toxin-producing E. coli and Salmonella.
<P>Cattle feces are a major source of contamination of beef products, produce, and recreational and drinking water. Despite rigorous surveillance of meat processors by the USDA Food Safety and Inspection Service, the number of confirmed human illnesses caused by E. coli O157:H7 and Salmonella continues at unacceptable levels. Control strategies aimed at reducing the prevalence of E. coli O157:H7 and Salmonella in cattle and swine, thus reducing the overall number of bacteria entering both the food and environmental pathways, may be the most effective approach for reducing the risk of human infections. Antimicrobial resistance is a naturally occurring biological phenomenon amplified because of misuse and overuse of antimicrobial drugs.
<P>The proposed research would greatly enhance our understanding of the ecology of E. coli O157:H7, Salmonella, and antimicrobial resistant bacteria in cattle and swine, including contamination of carcasses at slaughter, and provides an opportunity to evaluate existing and novel intervention strategies to mitigate risks associated with foodborne pathogens.
APPROACH: In the first objective, methods to detect E. coli O157 and Salmonella serotypes will be based on cultural procedures. We will evaluate the potential use of PCR-based (single or multiplex) procedure to initially screen samples. In the second objective, factors affecting gut persistence and fecal shedding will be determined in one more of the following ways: a. Natural prevalence field studies: Samples (feces, hide, or carcass) will be collected from feedlot cattle during the finishing phase or at a slaughter plant after cattle are slaughtered. b. Natural prevalence experimental studies: A large population of cattle will be prescreened and a subset of cattle confirmed as persistent shedders of E. coli O157 or Salmonella will be assigned to treatments. Experimental challenge studies: Cattle or swine in this study will be prescreened to assess the negative status for E. coli O157 or Salmonella and then orally inoculated with a cocktail of nalidixic acid-resistant E. coli O157 and Salmonella strains to determine the influence of various factors of interest. In vitro Fermentation studies: Batch-culture fermentation systems with ruminal microbial or fecal microbial inoculum will be used to test the effects of various factors (diets and dietary ingredients, feed additives, etc) on survival or growth of E. coli O157:H7 or other pathogens. For the third objective, control strategies aimed at reducing the prevalence of E. coli O157:H7 in cattle feces, thus reducing the overall number of bacteria entering both the food and environmental pathways, may be the most effective approach for reducing the risk of human infections. This is a multi-step effort; potential management factors and production practices are initially identified in our studies on the ecology of E. coli O157 and Salmonella, and then these factors and practices will be structured into formal hypotheses for evaluation. In the objective 4, the effect of antibiotics and metals on the antimicrobial susceptibilities of foodborne pathogens (E. coli O157, Salmonella and Campylobacter) and commensal (E. coli and Enterococcus spp.,) bacteria in feces of cattle and swine will be studied. Antimicrobial susceptibility patterns of all isolates will be determined by microbroth dilution method manually or using automated commercial systems. Real-time PCR will be used to quantify specific antimicrobial resistance genes in feces.