Conditioned pathogenicity of Microsporum gypseum biochemical mutants

Experimental infections of guinea pigs with three biochemical mutants of Microsporum gypseum are described. Under normal conditions the mutants are avirulent. The virulence became manifested in two mutants (1) when substance necessary for growth of individual mutants were brought into the place of inoculation, (2) when the defense mechanism of the organism was altered with the application of immunosuppressive drugs. One of the mutants was permanently avirulent. The importance of experimental results for explanation of conditioned pathogenicity of some dermatophytes is discussed.