1. Identify the environmental drivers impacting the presence and variability of Salmonella enterica serotypes and other common food borne pathogens within local, natural, multi-use poultry production systems. 2. Determine the linkage between phenotypes and genotypes of Salmonella enterica to find markers associated with colonization or invasion in chickens, as well as patterns of antibiotic resistances present in the poultry production environment. 3. Test mixtures of Salmonella enterica serotypes that vary in their ability to invade and colonize hens to determine the ability of commensal-like serotypes reduce the ability of pathogenic serotypes to colonize and persist. This information will be used to assess and improve vaccination strategies and reduce the use of antibiotics. 4. Determine the impact of infectious dosage of the various Salmonella enterica isolates on their ability to colonize and persist in egg-laying hens to facilitate their detection and reduction in poultry.