Role of Chrysosporium keratinophillum in the parasitic evolution of dermatophytes

Anti-dermatophytic activity of Chrysosporium keratinophillum against species of the genera Trichophyton, Microsporum and Epidermophyton floccosum was tested in vitro. When C. keratinophillum and different species of dermatophytes were inoculated on Sabouraud's dextrose agar plates 2 cm apart, no antagonistic effect of C. keratinophillum on the mycelial growth of dermatophytes was observed. However, conidia production was not observed on the hyphae of Trichophyton rubrum, Trichophyton tonsurans and E. floccosum grown near C. keratinophillum. The secretory substances released by C. keratinophillum inhibited the growth of T. rubrum, T. tonsurans, Trichophyton mentagrophytes var. interdigitale and E. floccosum at a concentration of 2,000 microg ml(-1) when tested by broth dilution technique. No inhibition of the growth was observed for Microsporum gypseum and Microsporum nanum. The anti-fungal activity of secretory substances released by C. keratinophillum was recorded to be heat stable. Results of the present study suggest that the anti-dermatophytic activity of the secretory substances of C. keratinophillum on T. rubrum, T. mentagrophytes var. interdigitale, T. tonsurans and E. floccosum may be responsible in part, for the absence of these dermatophyte species in soil. Considering the global prevalence of C. keratinophillum in soil one may speculate that the anti-dermatophytic activity of C. keratinophillum is one of the early events for the evolutionary divergence of saprophytic archi-dermatophytes to obligate parasitic dermatophyte species.