Fucofuroeckol-A from edible marine alga Eisenia bicyclis to restore antifungal activity of fluconazole against fluconazole-resistant Candida albicans

Phlorotannins from the brown alga, Eisenia bicyclis, are known to possess strong antimicrobial activity against several microbial pathogens. In this study, the antifungal activity of phlorotannins against Candida albicans was evaluated. Among the six phlorotannins tested in the present study, fucofuroeckol-A (FF) exhibited potent antifungal activity with minimum inhibitory concentration (MIC) value of 512 mu g mL(-1) against C. albicans strains. It is also observed that FF restored the antifungal effect of fluconazole against fluconazole-resistant C. albicans in the combination mode. The MIC values of fluconazole against C. albicans strains drastically decreased by three- to fourfold in the combination of FF-fluconazole. Furthermore, analysis of fractional inhibitory concentration (FIC) indices revealed that the median I FIC pound against C. albicans strains ranged from 0.287 to 0.508 with FF-A and fluconazole combination indicating synergistic antifungal effects with restoring antifungal activity of fluconazole. The results obtained in this study imply that phlorotannins especially FF derived from E. bicyclis can be a potential source to develop an antifungal agent against drug-resistant C. albicans infection.