The effect of bacterial surface structures on the pathogenesis of Salmonella typhimurium infection in chickens.

Mutants of Salmonella typhimurium strain SR11 containing Tn10 insertions in genes encoding for the motility and fimbriation phenotypes were evaluated for adhesion, invasion, and virulence in avian models. Mutations abolishing mannose-sensitive or mannose-resistant hemagglutination did not influence adherence or invasion in epithelial cells in vitro. A double hemagglutinin-deficient mutant, lacking both mannose-sensitive and mannose-resistant hemagglutinins, was diminished in ability to adhere to chick kidney epithelial cells in vitro, but invasion in vitro was not significantly affected. Compared with the wild-type parent, mutations that decreased motility reduced invasion levels in vitro and increased the peroral LD50 in one-day-old chicks. A mutant deficient in both motility and mannose-sensitive hemagglutination was greatly reduced in its ability to invade epithelial cells in vitro and persist in the liver and spleen of orally challenged chicks. Results of this study indicate that loss of motility in S. typhimurium attenuates peroral virulence in chicks.