Strong correlation between the antifungal effect of amphotericin B and its inhibitory action on germ-tube formation in a Candida albicans URA⁺ strain.

The hypothetical capacity of amphotericin B to suppress the formation of germ-tubes, which is the first step of yeast-to-hypha conversion in Candida albicans, has been investigated in the wild-type strain CEY.1 (CAI.4-URA⁺). Exponential cells exposed to concentrations of amphotericin B below or around the MIC90, exhibited a weak reduction in the percentage of human serum-induced germ-tube formation at 37ºC compared with a non-exposed control. However, the dimorphic transition was drastically suppressed after addition of potentially lethal doses of amphotericin B, which also caused severe cell killing. In contrast, an identical experimental approach carried out with the fungistatic compound 5-fluorocytosine had no significant effect on the level of the germ-tube formation. Together, these results strongly point to a close correlation between the fungicidal action of amphotericin B and its ability to impair morphogenetic conversion in C. albicans.