Lichen Polyphenolic Compounds for the Eradication of Candida albicans Biofilms

Lichens, due to their symbiotic nature (association between fungi and algae), constitute a chemical factory of original compounds. Polyphenolic compounds (depsides and depsidones) are the main constituents of lichens and are exclusively biosynthesized by these organisms. A panel of 11 polyphenols was evaluated for their anti-biofilm activity against Candida albicans biofilms on the maturation phase (anti-maturation) (MMIC50) as well as on preformed 24-h-old biofilm (anti-biofilm) (MBIC50) using the XTT assay. Minimum inhibitory concentrations of compounds (MICs) against C. albicans planktonic yeast were also determined using a broth microdilution method. While none of the tested compounds were active against planktonic cells (IC50 > 100 mu g/ml), three depsides slowed the biofilm maturation (MMIC50 <= 12.5 mu g/ml after 48 h of contact with Candida cells). Evernic acid was able to both slow the maturation and reduce the already formed biofilms with MBIC50 <= 12.5 mu g/ml after 48 h of contact with the biofilm. This compound shows a weak toxicity against HeLa cells (22%) at the minimal active concentration and no hemolytic activity at 100 mu g/ml. Microscopic observations of evernic acid and optimization of its solubility were performed to further study this compound. This work confirmed the anti-biofilm potential of depsides, especially evernic acid, and allows to establish the structure-activity relationships to better explain the anti-biofilm potential of these compounds.

Automated summary

Lichens, with their symbiotic nature of fungi and algae, produce unique polyphenolic compounds that show potential anti-biofilm activity against Candida albicans. Among these compounds, evernic acid stands out as an effective inhibitor of biofilm formation and maturation, showing low toxicity and no hemolytic activity at active concentrations.