Tolciclate is a thiocarbamic acid derivative with a potent antidermatophytic activity. The effects of the drug on the morphology of growing hyphae of Trichophyton mentagrophytes were studied with a high resolution scanning electron microscope. Control hyphae which were cultured for 48h without the drug grew vigorously. They had uniform widths and their surfaces were smooth. None of the cell debris was attached to the hyphal surface. In contrast, hyphae treated with the drug for 48 h showed four different types of morphologycal depending on the drug concentration, i) When grown with 0.02~0.3 ng/ml of the drug, no growth inhibition was noted, however, deformed, flattered and shrunken hyphae were occasionally observed, ii) When grown with a concentration of 1.3~< 20 ng/ml, incomplete growth inhibition occurred and elongation of hyphae was partially arrested. The hyphae were enormously swollen, iii) When grown at the fungistatic drug concentration (20~80mg/ml), most of the hyphae ceased to grow and profound shrinking and flattening were observed, iv) When incubated with the fungicidal drug concentration (≧320 ng/ml), they were enormously swollen and their cytoplasmic materials were released in great quantity into the medium. These dose-dependent morphological changes were discussed in connection with tolciclate's biochemical basis of action.
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