Growth and immunogenicity of photochromogenic strains of mycobacteria in the footpads of normal mice.

Specific pathogen-free CD-1 mice were infected subcutaneously in the footpad with mycobacterium kansasii, three strains of M. marinum, and two strains of M. simiae-habana, and the growth of the organisms in the footpad, the draining popliteal lymph node, and the lung and spleen was followed quantitatively for up to 60 days. The ability of a footpad inoculum of M. marinum to spread to the lungs and spleen correlated with the ability of the organism to survive and multiple at 37 C in vitro cultures. The amount of footpad swelling which developed in the M. kansasii- and M. marinum-infected mice varied depending upon the strain of organism and the size of the original footpad inoculum. Injection of dead M. marinum into the footpad also induced an extensive amount of swelling which varied with the strain used, as well as being dose dependent. M. marinum- and BCG-vaccinated mice were protected against a later footpad challenge with M. marinum or the highly mouse virulent M. tuberculosis strain ERDMAN. The significance of this finding is discussed in relation to cross-protection studies using a variety of mycobacteria in the footpad infection model.