Antifungal and Antibiofilm In Vitro Activities of Ursolic Acid on Cryptococcus neoformans

Ursolic acid (UA) exists in a variety of medicinal plants. UA exhibits antimicrobial activity against several microorganisms; however, little is known regarding the potential antifungal effect of UA on Cryptococcus neoformans (C. neoformans). The antifungal and antibiofilm activities of UA on C. neoformans H99 were evaluated in this study. Minimum inhibitory concentration (MIC) of UA against C. neoformans H99 was determined by microdilution technique, and its action mode was elucidated by clarifying the variations in cell membrane integrity, capsule, and melanin production. Moreover, the inhibition and dispersal effects of UA on biofilm formation and mature biofilms by C. neoformans H99 were evaluated using crystal violet (CV) assay, optical microscopy, field emission scanning electron microscopy and confocal laser scanning microscopy. The results indicated that the MIC value of UA against C. neoformans H99 was 0.25 mg/mL. UA disrupted the cell membrane integrity, inhibited the capsule and melanin production of C. neoformans H99 in a concentration-dependent manner. Further, UA presented the inhibitory effect on biofilm formation and dispersed mature biofilms, as well as compromised the cell membrane integrity of C. neoformans H99 cells within biofilms. Together, these results indicate that UA might be a potential therapeutic option for the treatment of C. neoformans-related infections.