[Active immunization to experimental salmonellosis in mice protective properties of Salmonella R mutants against infection with different pathogenic Salmonella species (author's transl)].

Mice (NMRI) were immunized twice with acetone-killed bacteria from 13 different Salmonella R-mutant and 6 Salmonella S form strains. Of the R mutants one strain was a semirough mutant, 9 strains belonged to the chemotype Ra, one to chemotype Rb2 and 2 to chemotype Re. Of the S forms 2 strains derived from serological group B, 2 from group D1 and one strain from each of group C1 and C2. Ten days after immunization the animals were challenged with increasing numbers of S-form bacteria (the same S strains as those used for immunization) administered intraperitoneally. The virulence (LD50) of the strains used was between 6 x 10(2) and 3 x 10(5) cells. The results show that every mutant was capable of affording protection to the S-form bacteria used, i.e. the protection was not confined to the species used for immunization; nevertheless differences in the degree of protection were present. These differences were found both in the ability of the different mutants to protect towards the same infecting microorganism and in the protection obtained by individual mutants towards infection with the different S-forms. With certain strains a relatively high degree of protection was obtained, with others the protection was low compared to that seen with homologous S form vaccines. In infection with s. typhimurium, unlike infection with other S-forms, the homologous R mutants were superior to the other mutants in their immunizing properties. Immunization with heterologous S-forms yielded similar results as those obtained with R mutants. S-forms with identical O-antigens were not necessarily comparable in their protective properties. Although the protective effect of R mutants was generally lower than that produced by homologous S-form vaccines, the present results show that in a few cases an equally high protection may also be obtained by R mutants. The present results lead to the conclusion that the cell-surface of Salmonella contains, in addition to the known antigens, other components playing an important role in inducing immunity to infection. A partial divergence in the pattern of such components among the different vaccines, would explain the extension of immunity obtained by the heterologous species also.