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<OL> <LI> Identify basic mechanisms and selective pressures involved in evolution and transfer of antibiotic resistance genes in enteric nonpathogens & pathogens particularly in relation to cattle and swine. <LI>Analyze, at the molecular level, the pathogenesis,epidemiology, and antibiotic resistance of Salmonella typhimurium DT104 and related pathogens obtained from cattle and swine. <LI>Evaluate possible associations between antibiotic resistance and expression virulence determinants in bacterial pathogens.
Culture media containing antibiotics used to enhance animal growth performance will be used to select for resistant bacterial species from the health swine intestinal tract. Resistance mechanisms will be characterized by molecular methods. The propensity of antibiotic resistance determinants to be transmitted to other bacteria, notably, foodborne pathogens, under various environmental conditions will be assessed. The molecular basis of S. typhimurium DT104 pathogenesis & epidemiology will be characterized by genetic examination, using PCR, of a national strain collection (~1,000 isolates). Strains will be screened for virulence markers, antibiotic resistance genes, phagetypes, as well as geographic patterns and host. Increased virulence, due coacquisition of antibiotic resistance genes & virulence genes, will be evaluated by identifying antibiotic resistance gene insertion sites. NADC, Ames, IA, PHFSEDR Lab; Bldg 2, B-1/A-5: BL-2: Pending