Damage to yeast cells of Cryptococcus neoformans by voriconazole and fluconazole: a culture and microscopic study.

A systematic cultural, cytological and microscopic study of voriconazole (VCZ) and fluconazole (FCZ) damage to Cryptococcus neoformans over time was made. When haemocytometer counts were compared with colony-forming units (cfu) viability decreased with increased drug concentration and prolonged treatment time up to 48 h. Percentage viability by vital staining correlated with cfu. Concentrations of VCZ were found to be 10-fold more potent than FCZ. At 72 h, percentage viability increased in cultures with lower drug concentrations, indicating outgrowth of surviving yeast cells. Drug treatment resulted in a cytological change in a large percentage of yeast cells characterized by a large central vacuole easily observed microscopically. Vital staining showed that there was no direct relationship between cytological changes and non-viability. These novel findings add a new approach for studying the antifungal action of VCZ and FCZ against C. neoformans and provide a new perspective on their antifungal action.