Ultrastructural alterations in Epidermophyton floccosum and Trichophyton mentagrophytes exposed in vitro to protoanemonin.

Protoanemonin (PrA) is an antimicrobial agent whose mechanism of action has not been clearly described. Some evidence exists which indicates that the compound inhibits growth by interacting with microtubules (MTs). In order to confirm this hypothesis, an ultrastructural study was undertaken in vitro on Epidermophyton floccosum and Trichophyton mentagrophytes, two dermatophytes which proved to be sensitive to the drug. A concentration of 1.25 x 10(-4) M (half-MIC dose) for 48 h, caused a series of ultrastructural alterations which were detected by scanning and transmission electron microscopy. Wave-like hyphae with distorted apical tips were frequently observed. Wall formation was variously affected as revealed by the deposition of incomplete septa and the accumulation of lomasome-like infoldings. An extrusion of extraparietal material binding adjacent filaments of the mycelia together was also produced. The nucleoplasm was characteristically crossed by MT-like structures. The possibility exists that PrA exerts its antifungal activity by MT interaction.