Growth of a highly virulent strain of Mycobacterium tuberculosis in mice of differing susceptibility to tuberculous challenge.

Mycobacterium tuberculosis strain CDC 1551 exhibited unusually high levels of infectivity and virulence during a recent outbreak of tuberculosis in a rural community. Mice infected intravenously or aerogenically with M. tuberculosis CDC 1551 developed infections in the lungs and spleen which were almost identical with those for M. tuberculosis strains Erdman, H37Rv and Indian. There was also no significant difference in the survival rates of mice infected intravenously with CDC 1551, Erdman or H37Rv over a 3-month period. Studies designed to detect differences in the growth rates of CDC 1551 and Erdman in 3 inbred strains of mice failed to explain the high level of infectiousness and virulence expressed by CDC 1551 in human populations exposed to this organism.