Immunity in Experimental Salmonellosis I. Protection Induced by Rough Mutants of Salmonella typhimurium.

Different rough mutants of Salmonella typhimurium were tested to determine their virulence and immunizing capacity when used as live vaccines for mice. All uridine diphosphate-galactose-4-epimeraseless mutants tested were much more potent immunizing agents than any other mutants. This capacity was not correlated with virulence or complexity of cell wall polysaccharide. For good protection, persistence of the rough strains in vivo was essential, but the protection lasted longer than the period during which bacteria were demonstrable in the liver and spleen of the mice. The outstanding immunizing capacity of the "epimeraseless" mutants is not dependent on the persistence of viable bacteria in the mouse.