[Infectivity and sensitivity to antibiotics of Rickettsia prowazekii mutants of the low-pathogenic strain E cultured in chick embryos]. / Infektsionnost' i chuvstvitel'nost' k antibiotikam mutantov Rickettsia prowazekii, malopatogennogo shtamma E, pri kul'tivirovanii v kurinykh émbrionakh.

Selection of mutants of a low pathogenic strain E of R. prowazekii is a trend in genetic investigation of this Rickettsia species and one of the approaches to stabilizing the strain avirulent properties with a purpose of using in vaccine prophylaxis of typhus. The mutants of R. prowazekii, strain E selected by the authors earlier were characterized with respect to their infective capacity for chick embryos (CE) and antibiotic sensitivity. It was found that the infective capacity for CE of the erythromycin resistant mutant induced by nitroso guanidine (EErrI) was by ID50 2-3 logarithms lower than that of the initial strain E. The infective capacity for CE of the rifampicin resistant mutant induced by nitroso guanidine (ERifrI) and the spontaneous erythromycin resistant mutant was similar to that of strain E. The ERifrI strain differed from the initial strain E by higher sensitivity to tetracycline and erythromycin and the EErrI strain differed from the initial strain E by higher sensitivity to tetracycline and rifampicin. It was shown that the biological properties of the nitroso guanidine-induced mutants resistant to rifampicin and erythromycin differed from those of the initial strain E and the properties of the spontaneous erythromycin resistant mutant were similar to those of the initial strain E.

[Biological properties of antibiotic-resistant mutants of the mildly pathogenic Rickettsia prowazekii E strain]. / Biologicheskie svoistva ustoichivykh k antibiotikam mutantov malopatogennogo shtamma E Rickettsia prowazekii.

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.

[Antibiotic sensitivity of the erythromycin-resistant strain E of Rickettsia prowazekii cultured in the vector's body]. / Izuchenie chuvstvitel'nosti k antibiotikam ustoichivogo k éritromitsinu shtamma E Rickettsia prowazekii pri kul'tivirovanii v organizme perenoschika.

Experiments on the laboratory cultures of lice infected by Weigl's method revealed that the spontaneous, erythromycin-resistant mutant of R. prowazekii strain E, adapted to the vector's organism, retained its resistance to erythromycin during 50 successive passages without the maintenance concentrations of this antibiotic. The above strain remained sensitive to tetracycline and levomycetin. Its level of sensitivity to the latter antibiotics was similar to that of R. prowazekii strains cultivated in the vector's organism for a long time.

[Production of the mutant E strain of Rickettsia prowazekii by mutagen exposure]. / Poluchenie mutantov shtamma E rikketsii Provatseka pri mutagennom vozdeistvii.

The possibility of obtaining the mutants of R. prowazekii, strain E, by exposing these organisms to the action of N-methyl-N-nitro-N-nitrosoguanidine was studied; this substance, used in doses of 5-10 micrograms, showed a mutagenic effect on rickettsiae suspended in physiological saline, after their exposure for 10-20 minutes at 37 degrees C. The mutants thus obtained proved to be resistant to erythromycin and rifampicin and were characterized by heterogeneity in the degree and stability of their antibiotic resistance. The effectiveness of selection was increased if mutagen-treated rickettsiae were selected after the first passage in chick embryos. The induced mutants differed from the original rickettsial strain by their lower infectiosity for chick embryos.