Fungicidal mechanism of action of D0870 against Cryptococcus neoformans under acidic conditions

The fungicidal mechanism of the triazole D0870 against Cryptococcus neoformans under acidic conditions was investigated. D0870 reduced the intracellular K+ content of C. neoformans at pH 4 to about half the value at pH 7 after 12 h of incubation. The 50% inhibitory concentrations of D0870 for ergosterol biosynthesis were almost the same at both pH 4 (0.017 microg/ml) and 7 (0.014 microg/ml); however, D0870 caused a marked accumulation of an unknown lipid and methylated sterols in C. neoformans cultured at pH 4. Extracted fractions containing the unknown lipid or methylated sterols showed strong fungicidal activities against C. neoformans both at pH 4 and 7 in phosphate-citrate buffer not containing D0870. Gas chromatographic-mass spectrometric analysis showed that the unknown lipid was obtusifolione. These results suggest that D0870 kills C. neoformans by disturbing the permeability of the cell membrane through the accumulation of obtusifolione and methylated sterols in the cell membrane under acidic conditions.