A replica plating technique for in vitro study of susceptibility of Candida albicans to miconazole, econazole and ketoconazole: some data for standardization.

We report our studies in vitro on the activity of ketoconazole (KZ), econazole and miconazole on 115 isolates of Candida albicans of clinical origin tested by an agar dilution method with three different culture media: yeast morphology agar, Sabouraud maltose agar and Casitone agar (CA). The antifungal effects of the imidazole compounds (IC) were strongest in CA. Eighty percent of the strains were inhibited by 0.1 micrograms/ml of KZ, the most active drug. The frequent appearance of "veil growth" at higher concentrations of the IC made the exact determination of the minimal inhibitory concentration (MIC) difficult. Microscopic examination of the growth on plates at the highest drug dilutions was performed and the results compared with a replica plating technique of IC plates on other plates with antibiotic-free media. The following were observed: a) a residual capacity of cell division of Candida strains even in the presence of high antifungal concentrations to which they are considered sensitive; and b) a certain viability (7% of the cases) of some fungal cells in the residual growth, particularly in those strains with higher conventional MIC. A standardized methodology is needed for the clinical evaluation of the susceptibility tests of Candida to the imidazolic compounds.