Proteins from Salmonella R-mutants mediating protection against Salmonella typhimurium infection in mice. II. Protection tests performed with proteins free from lipopolysaccharide.

Lipopolysaccharide-free proteins obtained from R-mutants of Salmonella typhimurium, S. minnesota and S. dublin as well as those from an S-form of S. typhimurium mediated protection in mice against experimental infection with S. typhimurium. The protection was measured by LD50 and is statistically significant. The level of protection of all the preparations was similar. Non-bacterial proteins had no effect under similar experimental conditions. Protection afforded by the purified proteins was lower than that of the corresponding complex crude extract; supplementation of proteins with lipopolysaccharide and phospholipids in model membrane vesicles enhanced their potency. However, lipopolysaccharides or phospholipids alone were not able to increase the efficacy of purified proteins. Some other fractions obtained by gel filtration of the crude extract also afford protection.