Impairment of virulence of in vitro subcultures of Mycobacterium lepraemurium.

Mycobacterium lepraemurium was cultivated in vitro on Ogawa egg-yolk medium. The pathogenicity of the third and eighth subcultures for C3H and C57BL mice was compared with that of in vivo grown murine bacilli by evaluating the mean survival time of infected mice. The results strongly suggest that a significant drop of virulence occurs during the in vitro cultivation of M. lepraemurium.