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

Skin microbiota, such as acne-related Cutibacterium acnes , Staphylococcus aureus , and fungal Candida albicans , 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 C. acnes , S. aureus , and C. albicans , 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 C. acnes , inhibited cell aggregation and hyphal formation by C. albicans , decreased lipase production, and increased hydrophilicity in S. aureus . In addition, shikonin at 5 or 10 µg/mL repressed the transcription of various biofilm-related genes and virulence-related genes in C. acnes and downregulated the gene expression levels of the quorum-sensing agrA and RNAIII , α-hemolysin hla , and nuclease nuc1 in S. aureus , 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.