The Inhibitory Effect of a Macrocyclic Bisbibenzyl Riccardin D on the Biofilms of Candida albicans

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Biofilm formation plays a key role in the life cycles and subsistence of many microorganisms. The human fungal pathogen Candida albicans has a high propensity to develop biofilms and resulted resistant to traditional antifungal agents. Biofilms are composed of a mixture of cell types, including yeast, pseudohyphal and hyphal cells, and hyphae are a prominent feature of biofilms. Riccardin D is a macrocyclic bisbibenzyl isolated from the liverwort Dumortiera hirsute in our laboratory. In the present investigation, the XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assay and live/dead cell staining were employed for evaluating the effects of riccardin D on C. albicans biofilms. The results demonstrated that riccardin D can interfere with the biofilm formation. To investigate whether this effect was due to the inhibition of hyphae formation, morphological observation and real-time reverse transcriptase polymerase chain reaction (RT-PCR) were employed for evaluating the effects of riccardin D on the hyphae formation and the expression of hyphae specific genes. The results showed that the hyphae formation was strongly inhibited and the mRNA expression levels of hyphae specific genes were downregulated after riccardin D treatment. We concluded that riccardin D interfered with the biofilm formation of C. albicans through downregulating the expression of hyphae specific genes and inhibiting the formation of hyphae.