Proteins from Salmonella R-mutants mediating protection against Salmonella typhimurium infection in mice. III. Separation and purification of soluble proteins and their use as vaccines and as precipitating antigens.

Urea extracts of Salmonella-S-form and R-mutant bacteria were separated into water-soluble and water-insoluble fractions and analysed with respect to their chemical composition. The main portion of proteins which at the same time represented the majority of the different polypeptides, was found in the water soluble fraction. This fraction, in the case of R-mutants, exhibited a considerably lower contamination with LPS and phospholipid than the total urea extract. This facilitated the further purification of proteins which could thus be carried out in urea-free buffer systems. In mice infected with S. typhimurium, the water soluble fraction afforded protection to the same extent as the total urea extract. The purified soluble proteins of Salmonella-R-mutants exhibited protective activity to injection with S. typhimurium and S. heidelberg comparable to that seen with the soluble extract. A species overlapping character of the protection became evident. In the Ouchterlony gel precipitation test, using the water soluble fraction and purified proteins as antigens, antibodies could be detected in rabbit immune sera and in sera of patients with Salmonella infections.