[The characteristics of the biological properties of capsule-free variants of Francisella tularensis]. / Kharakteristika biologicheskikh svoistv beskapsul'nykh variantov Francisella tularensis.

Comparative study of the properties of initial capsular (cap+) and non-capsular (cap-) F. tularensis strains has revealed that the non-capsular variants have their specific biological features. The characteristic features of these variants are avirulence and inability to produce an immunogenic effect in sensitive laboratory animals. Cap- mutants, depending on the method of their obtaining, may exhibit different sensitivity to some antibacterial preparations. In contrast to the initial virulent strains, cap- variants are intensively phagocytosed by peritoneal macrophages of white mice and capable of multiplication and survival in these macrophages. F. tularensis non-capsular forms are characterized by higher superoxide-dismutase and neuraminidase activity than the initial strains, which may be the explanation of the phenomenon of their intracellular survival. At the same time the main biochemical signs of cap- strains (citrullinureidase, phosphatase and penicillinidase) remain unchanged, which determines the possibility of their classification with this subspecies.

[The isolation of capsule-free variants of Francisella tularensis]. / Poluchenie beskapsul'nykh variantov Francisella tularensis.

New methods (selection in medium T with 20% Tween-80, inducing mutations leading to the appearance of resistance to triphenyl tetrazolium chloride or indoxyl phosphate) helped create a collection of F. tularensis stable non-capsular variants from strains of different subspecies. The characteristic features of all F. tularensis cap- variants include inability to serologic tests with erythrocytic diagnosticum, the absence of capsular antigens, sensitivity to normal human serum.

[Detection of persistent resistance to antibacterial drugs in various strains of Francisella tularensis]. / Obnaruzhenie persistiruiushchei ustoichivosti k antibakterial'nym preparatam u nekotorykh shtammov Francisella tularensis.

Under natural conditions, the Francisella tularensis strains AE-261 and P-13864 capable of forming the persist type of resistance to antibacterial drugs and being the cause of the infection in laboratory animals not responding to monotherapy with antibiotics were detectable. The antibioticograms of strains AE-261 and P-13864 under the in vitro conditions did not differ from those of the other studied strains responding to the antibiotic therapy. The observed phenomenon could be associated with individual peculiarities of the strains and their phenotypic variation in the host. Combinations of aminoglycoside antibiotics (streptomycin, gentamicin and amikacin) with rifampicin were shown to be highly active in the treatment of general forms of the infection due to such strains. The combined therapy of tularemia was also considered promising because of its high efficacy when the treatment was started at late periods as well as because unlike the monotherapy with the aminoglycoside antibiotics it provided complete elimination of the pathogen from the host.

[Pleiotropic nature of mutation of resistance to 2,3,5-triphenyl- tetrazolium chloride of Francisella tularensis]. / Pleiotropnyi kharakter mutatsii ustoichivosti k 2,3,5-trifenil- tetrazoliia khloridu u vozbuditelia tuliaremii.

Natural strains of F. tularensis were characterized by sensitivity to 2,3,5-triphenyl tetrazolium chloride (TTC). Development of TTC resistance in the cells of F. tularensis was accompanied by changes in the biological properties of the culture, i.e. the colony morphology, antigenic structure, virulence and immunogenicity for laboratory animals. Moreover, there was a direct correlation between the levels of TTC resistance and resistance to chloramphenicol, erythromycin, tetracycline, furazolidone and rifampicin. The antibiotic resistant mutants of F. tularensis were in turn more resistant to TTC than the initial strains. This could be useful in isolation of polymarked strains of F. tularensis for genetic studies and investigation of the nature of the phenomenon of virulence in F. tularensis.

[Comparative characteristics of biological properties of Francisella tularensis strains isolated in the USSR]. / Sravnitel'naia kharakteristika biologicheskikh svoistv shtammov Francisella tularensis, vydelennykh na territorii SSSR.

With a large collection of the strains of F. tularensis isolated it has been recently shown that cultures belonging to holarctica and mediaasiatica circulate in the endemic foci of the USSR. By their biological and genetic properties the natural strains of F. tularensis were homogeneous and represented type cultures of F. tularensis. Various ecological conditions in the natural environment did not change within the last 20 years the sensitivity of the tularemia microbe to the antibacterial drugs.