Antifungal Activity of Aureobasidin A in Combination with Fluconazole against Fluconazole-Resistant Candida albicans

Background: Aureobasidin A is known as a cyclic depsipeptide antibiotic with toxic effects against yeasts such as Candida spp at low concentration. Combination therapy is used as a conventional treatment for fungal infections, especially drug-resistant cases. The current study aimed to investigate the combined effects of fluconazole and Aureobasidin A on fluconazole-resistant C. albicans isolates using broth microdilution method. Materials & Methods: Antifungal activity of Aureobasidin A (AbA) compared to fluconazole against C. albicans ATCC 76615 strain was determined using the standardized broth microdilution method according to the Clinical and Laboratory Standards Institute (CLSI, document M27-Ed4) guidelines. The checkerboard method was used to test the combined effects of Aureobasidin A and fluconazole. The synergy, indifference, and antagonism were defined based on the fractional inhibitory concentration values below 0.5, 0.5-4, and more than 4 μg/mL, respectively. Findings: MIC50 and MIC90 evaluations of Aureobasidin A and fluconazole were done at concentrations of 0.25-2 and 32-64 μg/mL against C. glabrata isolates, respectively. The synergy between fluconazole and Aureobasidin A was observed against Candida isolate. A reduced MIC was demonstrated against C. albicans isolate when fluconazole was combined with Aureobasidin A at 4 to 0.12 μg/mL concentrations. Conclusion: The present study findings revealed that Aureobasidin A combined with fluconazole exhibited potent inhibitory effects against fluconazole-resistant C. albicans isolates. Further studies is recommended to investigate the synergistic effects of Aureobasidin A and other antifungal drugs