Determination of the in vitro activity of fluconazole against yeast strains using HPLC

The aim of this study was to evaluate the in vitro activity of fluconazole against two yeast strains by determining the fluconazole content via high-performance liquid chromatography (HPLC). Candida krusei ATCC 6258 and Saccharomyces cerevisiae were tested for fluconazole susceptibility by dilution tests. Fluconazole measurements by HPLC were performed in cultures of the strains at 6, 12, 24 and 48 h. In C. krusei ATCC 6258 cultures, 88.94% of the fluconazole was recovered at 48 h with respect to the level at time 0 h. The drug exhibited major activity at 12 and 24 h. An increase in cell number and elevated concentration of the drug were detected at 48 h. In S. cerevisiae cultures, the measurements revealed a fluconazole content of approximately 51.25% at 12, 24 and 48 h with respect to the level at time 0 h. However, the percentage of fluconazole detected and the minimal inhibitory concentration (MIC) value determined by agar dilution tests suggest a potential for fluconazole resistance in this susceptible strain. The decreases in fluconazole in C. krusei ATCC 6258 and S. cerevisiae cultures at each time point suggest a mechanism of resistance that is not correlated to efflux pumps.