Molecular and genetic characterization of Francisella tularensis strains of differing taxonomic status and virulence

Typing of Francisella collection strains by means of PCR on the basis of the tul4 gene coding the protein of the external membrane of 17kD and the genome region of differentiation RD1 is performed. The identification of the species and subspecies of 112 strains of Francisella tularensis was revealed. PCR on DNA targets’ loci of type IV pili genes—pilA, pilE2, pilE3, pilE4, pilE5, pilF, pilT, pilD, and pilQ—was carried out for differentiation of F. tularensis strains by virulence. The possibility was shown of distinguishing F. tularensis strains in PCR (primers A–B) on the basis of the uncovering of the gene pilA in virulent strains of three subspecies F. tularensis and F. tularensis subsp. novicida. The pilA gene was not detected in the vaccine strain 15/10 and its variants, as well as in most of avirulent F. tularensis supsp. holarctica strains. However, the fragment gene pilA was found in the attenuated strains F. tularensis subsp. tularensis and mediasiatica. No differences were found in other targets of pili genes between F. tularensis strains, with the exception of the strain F. tularensis subsp. novicida Utahl12, which did not have a fragment of the gene pilE2. The use of PCR to target the locus of the piliA gene allows differentiation of virulent F. tularensis subsp. holarctica strains from the vaccine 15/10, its variants, and avirulent strains.