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<ol> <li>Develop valid criteria for selecting indigenous cecal bacteria of swine and cattle that inhibit pathogenic bacterial growth (Salmonella, E. coli O157:H7);
<li>Develop defined cultures of indigenous cecal bacteria for use as direct-fed microbials to control salmonellosis and E. coli in swine and cattle; and
<li>Determine the mechanisms of the inhibition of Salmonella and E. coli growth.</ol>
Continuous-flow and static culture systems will be used to conduct metabolism studies with indigenous cecal bacteria and 14C radiolabelled lactose, glucose, glactose, and lactic acid. Bacteria that metabolize lactose, produce volatile fatty acids or other metabolites that are antagonistic to Salmonella and E. coli growth will be identified. Potentially protective mixed cultures of defined bacteria will be isolated and maintained in continuous-flow culture and tested in vitro and in vivo as direct-fed microbials to control Salmonella and E. coli colonization in new-born pigs at weaning and in cattle. Salmonella colonization resistance mediated by cytokines (local immune responses in the gut of swine and bovine) will be identified and characterized by affinity chromatography, polyacrylamide-gel electrophoresis.