Virulence of Mycobacteria tuberculosis

: The virulence of 43 Mycobacteria tuberculosis strains isolated from 21 patients with new cases of pulmonary tuberculosis and from 20 patients with chronic destructive pulmonary tuberculosis (CDPT) was studied in non-inbred albino mice. Twenty four (56%) and 19 (44%) M. tuberculosis strains belonged to the Beijing and individual genotypes, respectively. The virulence of isolates from the new cases of pulmonary tuberculosis was higher than that from CDPT patients. The M. tuberculosis strains studied showed no correlation between the virulence, viability, and affiliation to a certain genotype. However, there was a lower rate of decreased virulence in multidrug-resistant strains of the Beijing genotype than in the isolates of individual genotypes. This is likely to be a factor of the high transmissible capacity of M. tuberculosis strains of the Beijing family.