Impact of pH on the antifungal susceptibility of vaginal Candida albicans

OBJECTIVE: To investigate the antifungal susceptibility at pH 7.0 and pH 4.0 of 5 antifungal agents against Candida albicans isolated from patients with vulvovaginal candidiasis. METHODS: Antifungal susceptibility testing at pH 7.0 and pH 4.0 was performed using the broth microdilution method (CLSI, document M27-A2). RESULTS: The minimal inhibitory concentrations (MICs) of miconazole, clotrimazole, fluconazole, and nystatin against C. albicans at pH 4.0 were significantly higher than those at pH 7.0 (0.25 vs 0.03 μg/mL, 0.50 vs 0.03 μg/mL, 0.50 vs 0.25 μg/mL, and 32 vs 2 μg/mL, respectively; P<0.001), whereas the MIC of itraconazole at pH 4.0 was lower than that at pH 7.0 (0.030 vs 0.125 μg/mL; P<0.001). The susceptibility rate of C. albicans to itraconazole at pH 4.0 was significantly higher than at pH 7.0 (95.0% vs 51.7%; P<0.001). The susceptibility rate to itraconazole at pH 7.0 was significantly lower than the susceptibility rate to fluconazole (51.7% vs 100.0%; P<0.001), whereas the susceptibility rates to the 2 drugs were similar at pH 4.0 (95.0% and 96.7%, respectively). CONCLUSION: Media at different pH values should be used for sensitivity tests according to the environment of C. albicans.