Anti-Acne Potential of <i>Quercus salicina</i> Extract: Inhibition of <i>Cutibacterium acnes</i> Growth and Virulence

Acne vulgaris is a prevalent inflammatory skin disorder mediated by <i>Cutibacterium acnes</i>, a key etiological factor. In this study, the anti-acne properties of the ethyl acetate fraction of <i>Quercus salicina</i> Blume (QsB-EE) against <i>C. acnes</i> were investigated. The QsB-EE fraction was separated into subfractions (E1-E6) using preparative HPLC. Antimicrobial and anti-virulence activities were evaluated via bacterial growth, biofilm, and lipase activity assays. Virulence gene expression was assessed using qRT-PCR, and bioactive compounds were identified by LC-MS/MS. The QsB-EE demonstrated significant antimicrobial (MIC 125 μg/ml) and strong anti-virulence effects. The E1 fraction was the most potent, exhibiting the lowest MIC (16 μg/ml), highest biofilm inhibition (86.19% at 1,000 μg/ml), and highest lipase inhibition (93.72% at 10 μg/ml). In addition, mechanistic studies confirmed that E1 significantly downregulated the expression of key virulence genes: <i>ppa</i>0149 (biofilm), <i>geh</i>A (lipase), and <i>hyl</i> (hyaluronidase). LC-MS/MS identified (+)-catechin as the major compound in E1, alongside kaempferol and quercetin in E5. Although further <i>in vivo</i> studies are warranted to evaluate the therapeutic efficacy, our findings suggest that QsB-EE possesses promising anti-acne potential by targeting <i>C. acnes</i> virulence factors through the active compounds concentrated in the E1 fraction.