Inhibition of adhesion-specific genes by Solidago virgaurea extract causes loss of Candida albicans biofilm integrity

Aims Candida albicans biofilms are commonly associated with severe oral infections. We previously discovered that a crude extract from the Solidago virgaurea plant (SV extract) was a potent inhibitor of C. albicans biofilm formation. Here, we further investigate the mechanisms underlying C. albicans biofilm inhibition by the SV extract. Methods and Results The SV extract was shown to inhibit laboratory and clinical C. albicans isolates adherence and hyphal transition on inert support and epithelial human cells, without affecting viability and growth of planktonic yeasts. Interestingly, RT-PCR-based experiments demonstrated that some key genes involved in adhesion and hyphal morphological switch (e.g. Hwp1p, Ece1p, Als3p) were strongly down-regulated by the SV extract. Moreover, antimicrobial synergy testing (checkerboard assay) demonstrated that antifungal effects of miconazole, nystatin or a common antiseptic mouthwash were synergistically improved when used in combination with the SV extract. Conclusions The SV extract prevents C. albicans biofilm formation through direct inhibition of key adherence and hyphae-associated genes. Significance and Impact of the Study Biofilm is considered as a key virulence factor of C. albicans infection. Our discovery of an inhibitor specifically acting on genes involved in biofilm formation paves the way for the future development of a new class of antifungal product.