Distribution of mating types among clinical isolates of the Microsporum gypseum complex.

Forty-five clinical isolates of Microsporum gypseum were crossed with the + and - tester strains of Nannizzia gypsea, N. incurvata and N. fulva to determine their mating type. Thirty-two produced fertile gymnothecia when crossed with N. gypsea, of which 13 reacted as + and 19 as -. Ten produced fertile gymnothecia when crossed with N. incurvata, of which 7 reacted as + and 3 as -. The remaining 3 were sterile in all crosses with N. gypsea. N. incurvata and N. fulva. Of these 3, 2 were fluffy, degenerated cultures of M. gypseum, and the other one appeared to bae identical with the description of M. gypseum var. vinosum in cultural and morphological characteristics. There was approximately a 1:1 overall ratio of mating types among a total of 90 clinical isolates of M. gypseum in Japan on the basis of the above results and the data recently reported in the literature by other Japanese workers. The present results suggest that the ability to cause skin infection of humans by the soil-inhabiting organisms is approximately equal in the mating types and probably independent of sexuality.