In vitro susceptibility of Trichophyton rubrum isolates to griseofulvin and tioconazole. Induction and isolation of a resistant mutant to both antimycotic drugs. Mutant of Trichophyton rubrum resistant to griseofulvin and tioconazole.

The in vitro susceptibility of three clinical Trichophyton rubrum isolates to griseofulvin and tioconazole, determined by the minimal inhibitory concentration (MIC), was 2 and 0.5 to 1.0 micrograms/ml, respectively. One mutant (gril) obtained after mutagenic treatment of one of these isolates was selected and showed simultaneous resistance to griseofulvin (MIC > 2000 micrograms/ml) and tioconazole (MIC = 1.0 microgram/ml). The clinical importance and the possibility of a multidrug resistance (MDR)-type mechanism being involved in this event is discussed.