Morphogenetic effect of L-cysteine on dermatophytes.

In the presence of L-cysteine, all the 24 dermatophyton fungi under study grew poorly. None of the strains, except Trichophyton menatographytes var. quinckeanum, grew in the presence of 0.04 M L-cysteine. The strains growing on a medium containing L-cysteine showed morphological changes. The surface of the colonies lost its velvety appearance and became awnless or waxy. The strains grown in the presence of L-cysteine abundantly formed chlamydospores. The chains of chlamydospores may resemble yeast cell chains, but true budding forms were not found in cultures in vitro. If strains precultivated on L-cysteine-containing medium were injected intraperitoneally into mice budding forms appeared in the peritoneal fluid.