Effect of licorice compounds licochalcone A, glabridin and glycyrrhizic acid on growth and virulence properties of Candida albicans.

Candida albicans is the predominant causal agent of candidiasis. Its ability to form hyphae and biofilm has been suggested to be key virulence factors. In this study, we investigated the effect of major licorice compounds licochalcone A, glabridin and glycyrrhizic acid on growth, biofilm formation and yeast-hyphal transition of C. albicans. The synergistic effect of licorice compounds with the antifungal drug nystatin was also evaluated. Minimal inhibitory concentrations (MICs) for C. albicans were determined using a microplate dilution assay. The synergistic effect with nystatin was determined similarly. The effect of licorice compounds on biofilm formation was evaluated using a microplate assay and crystal violet staining. The effect of licorice compounds on yeast-hyphal transition was determined by microscopic observation. The toxicity of licorice compounds towards oral epithelial cells was evaluated with an MTT assay. Glabridin and licochalcone A showed antifungal activity on C. albicans while glycyrrhizic acid had no effect. Complete growth inhibition occurred with sub-inhibitory concentrations of nystatin with either glabridin or licochalcone A. Biofilm formation was inhibited by 35-60% in the presence of licochalcone A (0.2 μg ml(-1)). A strong inhibitory effect (>80%) on hyphal formation was observed with licochalcone A or glabridin (100 μg ml(-1)). Glabridin and licochalcone A at high concentrations showed toxicity towards oral epithelial cells. In summary, glabridin and licochalcone A are potent antifungal agents and may act in synergy with nystatin to inhibit growth of C. albicans. Licochalcone A has a significant effect on biofilm formation, while both licochalcone A and glabridin prevented yeast-hyphal transition in C. albicans. These results suggest a therapeutic potential of licochalcone A and glabridin for C. albicans oral infections.