Cryptococcus neoformans: the model organism for yeast antifungal drug susceptibility testing.

We describe an approach to antifungal susceptibility testing of the yeast Cryptococcus neoformans that shows promise for predicting the mycological response in patients to treatment. Quantitative cultures of the cerebrospinal fluid provide a direct measure of the patient's mycological response to treatment and have been used in multiple studies to identify the most promising antifungal drugs for subsequent testing in larger clinical studies. Using these quantitative measures of response, a modified macrobroth dilution assay system shows the potential for predicting the response of an individual patient to treatment with amphotericin B, fluconazole, or the combination of amphotericin B plus flucytosine. We describe this modified macrobroth dilution assay method, the statistical approach for assessing susceptibility, and the clinical decisions that can be guided by this in vitro antifungal drug susceptibility testing.