Aberrant development of Trichophyton mentagrophytes hyphae cultured in the presence of Congo red

When Trichophyton mentagrophytes colonies were placed on a medium containing 150 micrograms/ml of Congo red, a dye which prevents chitin fibrillogenesis, their growth rate was reduced. The newly formed mycelium, examined under an ultraviolet microscope, consisted of thick, curled and branched hyphae endowed with swollen tips and subapical bulges. Short-time exposure revealed that the major sites of dye accumulation were the extension zones. Normally structured hyphae arose from aberrant mycelia when they were transferred onto a dye-free medium. The phenomena observed suggest that Congo red alters the wall properties of the extension zone, by inhibiting the gradual conversion of chitin chains, synthesized at the extreme tip, into microfibrils of increasing size and density.