Inhibition of Biofilm Formation in Cutibacterium acnes , Staphylococcus aureus , and Candida albicans by the Phytopigment Shikonin

Skin microbiota, such as acne-related , , and fungal , can form polymicrobial biofilms with greater antimicrobial tolerance to traditional antimicrobial agents and host immune systems. In this study, the phytopigment shikonin was investigated against single-species and multispecies biofilms under aerobic and anaerobic conditions. Minimum inhibitory concentrations of shikonin were 10 µg/mL against , , and , and at 1-5 µg/mL, shikonin efficiently inhibited single biofilm formation and multispecies biofilm development by these three microbes. Shikonin increased porphyrin production in , inhibited cell aggregation and hyphal formation by , decreased lipase production, and increased hydrophilicity in . In addition, shikonin at 5 or 10 µg/mL repressed the transcription of various biofilm-related genes and virulence-related genes in and downregulated the gene expression levels of the quorum-sensing and , α-hemolysin , and nuclease in , supporting biofilm inhibition. In addition, shikonin prevented multispecies biofilm development on porcine skin, and the antimicrobial efficacy of shikonin was recapitulated in a mouse infection model, in which it promoted skin regeneration. The study shows that shikonin inhibits multispecies biofilm development by acne-related skin microbes and might be useful for controlling bacterial infections.