[Characterization of the recombinant strain Francisella tularensis R1A].

For the first time F.tularensis recombinant strain R1A, obtained by the transfer of genes responsible for virulence in F.tularensis strain B 399 A-Cole into recipient cells of the R-form, was studied. Strain R1A was characterized by morphological, tinctorial and biochemical properties, similar to those of F.tularensis virulent strains, and became resistant to the bactericidal action of animal sera, as well as heat resistant (tr42). The results of animal experiments revealed that strain R1A proved to be highly virulent for noninbred white mice, faintly virulent for guinea pigs and avirulent for rabbits. In contrast to the R-form, recombinant strain R1A exhibited high antigenic activity, as well as partially protected guinea pigs from 100 DCL of F.tularensis highly virulent strain B A-Cole. The totality of its properties places recombinant strain R1A in an intermediate position between F.tularensis virulent and vaccine strains.