Stimulating effect of pyruvate on the growth of Mycobacterium leprae in cell-free, semisynthetic, soft agar medium

A bacterial suspension prepared from a nodule from a patient with lepromatous leprosy was inoculated into the cell-free, semisynthetic, semiliquid agar medium M-Y 11d-modified from the authors' medium M-Y 1c by omitting glycerol and adding pyruvate-and incubated at 37 degrees C. The growth of the organism was stimulated so markedly that after about 50 weeks' incubation of the primary culture microcolonies could be seen floating in the agar layer as tiny white particles, while the medium fluid assumed a yellow tinge. These macroscopic colonies were sucked up by pipette and subjected to microscopic examination. A bacterial suspension prepared from the first subculture of this strain by centrifugation elicited the same skin reactions in leprosy patients as did the standard Mitsuda's antigen. The organism in the culture was therefore identified as M. leprae.