Our objective in this application is to determine the mechanisms underlying dietary impacts on E. coli O157 shedding in cattle. The central hypothesis for the proposed research is that different feed components provide specific nutrients to the hind gut that influence microbial populations that either promote or suppress E. coli O157 carriage by cattle.
Aim 1: Compare the impact of DGs (DG) and a corn-based ration on colonic carbohydrate composition and E. coli O157 prevalence during the growing period of cattle. The working hypothesis of this aim is that feeding DG will alter the amount and composition of simple sugars available for bacterial uptake in the colon, creating a microenvironment that favors the survival of E. coli O157.<P>
Aim 2: Determine impact of DG on colonic microbial ecology of cattle. The working hypothesis of this aim that different feeds (DG vs. corn) will select for significantly different microbial populations. By profiling the microbial structure of colonic bacteria we will be able to determine the degree to which feed alters the community environment experienced by E. coli O157 just prior to, during and following shedding events.<P>
Aim 3: Determine the dynamics of bovine microbial colonic carbohydrate composition and microbial ecology following change from a DG-base diet to one based on corn. The working hypothesis of this aim is that certain microbial populations in the colon will act to suppress E. coli O157 colonization, survival, and subsequent shedding. Such populations may provide useful either as biological markers for shedding risk or active ingredients for new pre-biotics and probiotics.
NON-TECHNICAL SUMMARY: The project goals are to reduce the carriage (pathogen load) of E. coli O157 in beef cattle through feed interventions. We hypothesize that energy sources used in cattle feeds influence the carriage of E. coli O157 by making the colonic microenvironment and microbial ecology either more or less hospitable for the survival of this pathogen. We will compare the colonic microbial ecology between cattle feed corn- or distillers' grain- based diets and link the specific the changes in colonic microbial ecology with the presence and magnitude and E. coli O157 shedding among naturally exposed groups of cattle. Specific bacterial species that are associated with lower E. coli O157 shedding will be identified, isolated, and tested for in vivo inhibition of E. coli O157. Colonic mucin carbohydrate composition will be assessed and correlated with diets and E. coli O157 shedding. At the completion of this project we will have understanding of the mechanisms involved in dietary and colonic ecological influences of E. coli shedding by cattle. This information will provide preharvest intervention strategies in the selection of feed sources or additives that will optimize food safety. The successful completion of this project will enhance the safety of the food supply and reduce foodborne illnesses.
<P>APPROACH: This is a prospective longitudinal cohort study that will compare E. coli O157 and other fecal microbial communities among cattle fed differing diets, specifically corn-based and distiller's grain based diets. Immunomagnetic seperation will be used to assess fecal O157 carriage. Terminal restriction fragment legnth polymorphisms will be used to compare microbial population in fecal samples. Correlations between microbial communities (and specific microbial populations,E. coli O157 presence and diet will be performed. Specific populations that are negatively correlated with E. coli O157 will be considered as possible inhibitors this organism.