Assay for yeast susceptibility to 5-fluorocytosine and amphotericin B in a frozen microtiter system.

A microtiter plate method for determining susceptibility of yeasts to 5-fluorocytosine and amphotericin B, which uses color indicators to detect end points, is presented. The microtiter plates can be made in advance and stored frozen for at least eight weeks. Forty-two isolates of Candida albicans, 12 of Candida tropicalis, and nine of Torulopsis glabrata were tested. Results showed good correlation with turbidity tube dilution susceptibility testing methods. The microtiter method is stable, easy to use, accurate, and reproducible. Studies with four strains of Cryptococcus neoformans showed that the organism could not be tested by this method because growth was slow and there was insufficient acid production.