[Chemical and biological properties of revertants derived from a Salmonella typhimurium Rd1-mutant (author's transl)].

Two S-form-revertant strains were isolated from a S. typhimurium Rd1 culture on account of their phage resistance. In microbiological and serological (O-agglutination) characterization - as well as in stability tests (agglutination in auramin and saline and heating at 100 degrees C) - the behaviour of the two strains was the same as that of the wild type. The two strains were found to be indistinguishable from the wild type strain also with respect to the chemical composition of their lipopolysaccharides. Thus the amount and proportion of fatty acids and sugar residues as well as the number of repeating units in the O-chain were all identical. In contrast, the isolated revertants were similar to the Rd1 mutant with respect to their auxotrophic markers methionine and tryptophane, to the absence of flagella as well as to the reduced content of cyclopropane fatty acids (C17, C19). Protein analysis revealed no significant qualitative or quantitative differences between the wild type strain and the two revertants with respect to the major proteins of their outer membranes. The sensitivity of the revertants to crystal violet, erythromycin and rifamycin SV was intermediate between the wild type and the Rd1 mutant. Their temperature maximum in nutrient broth was 43 degrees C, the retardation in growth at this temperature corresponding to that of the Rd1 mutant. At 37 degrees C, however, the growth rate of the revertants was identical to that of the wild-type, while that of the Rd1 mutant was slower. Addition of sodium chloride to the growth medium rendered the temperature dependent behaviour of the mutants and revertants similar to that of the wild type. Studies in NMRI mice revealed that the revertants, also with regard to their virulence, occupy an intermediate position between the mutant and the wild type. Nevertheless their ability to afford protection to Salmonella typhimurium infection following active immunization with acetone killed cells was as high as that of the wild type. The results show that the biologic behaviour of S. typhimurium is determined by the type of lipopolysaccharide it contains but also to a large extent by other cell-wall constituents.