Growth rate of mycobacteria in mice as an unreliable indicator of mycobacterial virulence

Abstract

The CDC1551 strain of Mycobacterium tuberculosis was compared with the H37Rv strain of M. tuberculosis and the Ravenel strain of Mycobacterium bovis for virulence in mice. Although all three strains gave rise to the same level of stationary infection in major organs, mice infected with the Ravenel strain died much earlier from lung disease.

FIG. 1

Time course of infection with CDC1551, H37Rv, and Ravenel in C57BL/6 mice infected via the respiratory route with approximately 10² CFU. The strains were almost identical in their ability to grow in the organs of mice. Means for five mice per group per time point ± standard deviations are shown.

FIG. 2

Survival of times of 10 mice infected by aerosol with 10² CFU of CDC1551, H37Rv, or Ravenel. Mice infected with Ravenel died with a median survival time of 115 days. The experiment was terminated before mice infected with the other strains had all died.

FIG. 3

Appearance of the lungs of mice infected by aerosol with approximately 10² CFU of CDC1551 (right), H37Rv (left), or Ravenel (center) on day 120 of infection. Ravenel caused the most lung pathology, followed in turn by H37Rv and CDC1551.