Impact of M. tuberculosis genotype on survival in mice with experimental tuberculosis

: To study the virulence of Mycobacterium tuberculosis strains of the W cluster, C57B1/6 mice were intravenously inoculated with a lethal dose (5x10(6) CFU) of 14 clinical M. tuberculosis strains (11 drug-sensitive and 3 multidrug-resistant) belonging to different RFDP IS6110 genotypic clusters and two laboratory M. tuberculosis strains H37Rv and H37Ra. The virulence was evaluated by the survival of mice after infection and by the trends in body weight loss. The study indicated that the mice inoculated with different M. tuberculosis strains differed in survival rates and in the trend in body weight loss. A minor HD cluster strain and 2 non-clustered strains were most virulent, next were 2 AI cluster strains. W cluster strains had both higher (n = 2) and lower (n = 3), and comparable (n = 2) H37Rv virulence. A KQ cluster strain had the least virulence. An attenuated H37Ra strain caused no animal death. Inoculation with three multidrug-resistant strains belonging to the W cluster (n = 2) and one non-clustered strain demonstrated no relationship of virulence to the sensitivity of a strain to antituberculous agents. The findings argue against the opinion on W cluster M. tuberculosis strains as hypervirulent.