Protective activity of extracts from Salmonella-R-mutants against Salmonella typhimurium infection in mice. Influence of repeated extractions on the chemical composition and efficacy of the extracts.

Repeated extractions (three times) of an S-form and different R-mutants of S. typhimurium and S. minnesota with urea medium resulted in extracts varying in their chemical composition with respect to protein, lipopolysaccharides, phospholipids and nucleic acids. Protein appeared to be the major component of all the extracts and was present in substantial amounts in the third extract also. With subsequent extractions the lipopolysaccharide and phospholipid contents generally decreased in the R-mutants, but increased in the S-form. The nucleic acid contents always increased with repeated extractions. polypeptide patterns of the materials obtained after repeated extraction showed some differences in case of R-mutants predominantly. Active immunization of mice with these extracts protected them almost to the same extent against S. typhimurium infection. Only in case of one R-mutant a graded decrease in protection could be observed from extract 1 to extract 3. However, the differences in composition of the vaccines based on chemical analysis data and polypeptide pattern could not account for this decrease in protection.