Research on Persistent Colonization of Pigs by Salmonella typhimurium and the Effects of Transportation Related Stress on Shedding of Salmonella typhimurium

Isaacson, Richard
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Research in my laboratory has been on the mechanism(s) employed by Salmonella typhimurium to persistently colonize pigs and on the factors contributing to increased shedding of S. typhimurium by pigs at slaughter. A phenotype of S. typhimurium has been identified that attaches to epithelial cells isolated from the pig small intestine. Cells of the adhesive phenotype produce pili that may be the adhesin, while cells of the non-adhesive phenotype do not. Cells of the adhesive phenotype also produce 10-12 unique envelope proteins and several new surface antigens. Adhesive cells are more readily phagocytized by porcine neutrophils and macrophages and have a much greater degree of intracellular survival in the phagocytic cells. Cells can readily shift between the two phenotypes. In the laboratory the rate of change is between 10-2 and 10-4. When pigs were challenged with cells in the nonadhesive phenotype, only cells in the adhesive phenotype were recovered from pigs. Both phenotypes were of equal virulence. This demonstrates that the adhesive phenotype is important in pigs. A nonadhesive mutant was isolated and shown to be less virulent in mice and was more rapidly cleared from the intestinal tract of pigs. The role of the adhesin and the other properties associated with the adhesive phenotype are being investigated with the intent of learning how pigs can be long term carriers of S. typhimurium.