Increased sensitivity of Candida albicans cells accumulating 14 alpha-methylated sterols to active oxygen: possible relevance to in vivo efficacies of azole antifungal agents.

The sensitivity of Candida albicans cells to killing by hydrogen peroxide was found to increase markedly when they were grown in the presence of sub-growth-inhibitory concentrations of the azole drug clotrimazole (CTZ). A superoxide anion-generating system consisting of xanthine and xanthine oxidase also killed such CTZ-treated cells more efficiently than control cells, but this seemed to be accounted for by hydrogen peroxide secondarily formed from superoxide anion as judged by the effect of catalase and superoxide dismutase. The increased sensitivity to hydrogen peroxide was considered to be attributable to the inhibition of 14 alpha-demethylation of ergosterol biosynthesis by CTZ, since a 14 alpha-demethylation-deficient mutant of C. albicans exhibited a similar phenotype. It is suggested that the in vivo efficacy of azole antifungal agents against C. albicans infection is at least partially due to the sensitization of the fungal cells to the oxygen-dependent microbicidal system of the phagocyte.