Antifungal activity of Sapindus saponins against Candida albicans: interruption of biofilm formation

Candida albicans was a common fungal pathogen, which usually existed on the surface of many organs and causes many diseases. In this study, anti-Candida albicans biofilm activity of Sapindus mukorossi Gaertn were evaluated. Amount of biofilm was determined by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide colorimetric assays. The effect of Sapindus saponins on Candida albicans 10231 was observed by confocal laser scanning microscope, scanning electron microscope, and inverted fluorescence microscope. To further understand the antibacterial mechanism of Sapindus saponins against C. albicans biofilm, the expression levels of specific expression genes (ECE1, ALS3, and HWP1) and transcription regulation genes (NRG1) related to mycelium and adhesion were determined. The results showed that 0.16 mg/mL of Sapindus saponins could inhibit early-formed biofilm (77.6%) and 0.64 mg/mL of Sapindus saponins could inhibit mature biofilm (55.7%). Further study showed that Sapindus saponins could inhibit formation of biofilm by preventing aggregation of C. albicans, destroying surface morphology, especially inhibiting transformation of mycelium. Also, 0.16 mg/mL of saponins could significantly reduce hydrophobicity and adhesiveness of surface, which would be detrimental to accumulation of biofilm on substrate surface. Further gene expression tests revealed that the Sapindus saponins could down regulate two genes involved in adhesion and hyphe growth (ALS3 and ECE1). Overall, Sapindus saponins showed promising antibiofilm activity, which could be considered as a possible option for the treatment of candidiasis associated with biofilm formation in the future.