Morphological study of Trichophyton rubrum: ultrastructural findings after treatment with 4-amino-3-methyl-1-phenylpyrazolo-(3,4-c)isothiazole.

The antifungal activity of 4-amino-3-methyl-1-phenylpyrazolo-(3,4-c)isothiazole was studied on Trichophyton rubrum. The compound, at concentrations between 20 and 10 microg ml(-1), induces a remarkable reduction in the growth and causes deep morphogenetic anomalies. The ultrastructural modifications have demonstrated that the compound targets the cell membrane of the fungus, breaking down not only the endomembrane system, but also the 'outer' membrane, with consequent extrusion of materials in the medium. The results suggests a mechanism of action similar to other azoles clinically utilized.