[Biological properties of antibiotic-resistant mutants of the mildly pathogenic Rickettsia prowazekii E strain].

The use of R. prowazekii strain E with low pathogenicity as live vaccine against exanthematous typhus is limited by its high specific reactogenicity, which is probably due to the reversion of the virulence of the strain. One of the approaches to the stabilization of the avirulent properties of strain E is obtaining its mutants with stable decreased pathogenic properties. The article presents the data on the infectious properties of R. prowazekii antibiotic-resistant strain E mutants obtained in earlier experiments, in respect of chick embryos and laboratory animals, as well as the capacity of this strain for producing immunity to challenge with R. prowazekii virulent strain in guinea pigs. The study has revealed that the erythromycin-resistant mutant of R. prowazekii strain E, induced by nitrosoguanidine (NG), has lower infective capacity for chick embryos, guinea pigs, cotton rats and white mice. The infective capacity of the NG-induced rifampicin-resistant and spontaneous erythromycin-resistant mutants of R. prowazekii strain E is similar to the infective capacity of the initial strain. The rifampicin-resistant and spontaneous erythromycin-resistant mutants of R. prowazekii strain E possess immunogenicity similar to that of the initial strain E, and the NG-induced erythromycin-resistant mutant possesses lower, but sufficiently pronounced immunogenicity despite its decreased infective capacity for guinea pigs.