E. coli O157 causes over 73,000 foodborne illness cases annually and 60 deaths per year. The E. coli O157 problem begins with cattle. Indeed, bovine-origin food products are the primary vehicle of infection, cattle are the principal reservoir, and bovine fecal shedding is the primary mode of food contamination. Because of the importance of the bovine reservoir and fecal shedding to the disease epidemiology, the colonization of cattle by E. coli O157 has been extensively studied. Recently, the rectum was identified as a site of tropism for E. coli O157 colonization of adult cattle. However, the underlying factors impacting bovine colonization by E. coli O157 are not known. The overall objective of this research is to understand the bovine rectum-bacterial relationship with a goal to reduce bovine shedding of E. coli O157. This goal is consistent with NCBA’s priority to ‘build the knowledge base on the ecology and epidemiology of E. coli O157:H7 from preharvest to the harvest facility.’
The stated objectives for this work were:
1) Pre-harvest basic research to elucidate nutritional bases for colonization of the bovine rectum by E. coli O157. Factors fundamental to rectal colonization are incompletely understood and previous studies have focused on attachment factors. The principle method employed within this objective is in vivo co-colonization of cattle with wild-type E. coli O157 EDL933 and a collection of isogenic mutants deficient in sugar catabolism pathways. The occurrence and degree of a colonization defect in mutant strains will inform the investigator what nutrients are fundamental to the rectal colonization by E. coli O157. Knowledge of such nutrient preferences obtained from these experiments provides a basis for the next objective.
2) The second objective is aimed at intervention development. Prebiotic strategies are proposed that hypothesize that alteration of the nutrient availability of the rectal microenvironment by instillation of an abundance of a sugar non-essential to E. coli O157 will favor proliferation of commensal E. coli that prefer that specific sugar. Probiotic strategies are proposed that aim to co-colonize other bacteria that possess superior abilities to grow and/or catabolize a nutrient preferred by E. coli O157. Both prebiotic and probiotic strategies, in this context, are hypothesized to limit or eliminate E. coli O157 colonization by means of a phenomenon known as competitive exclusion or colonization resistance.
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