Skin commensal bacterium Staphylococcus epidermidis CCSM0287 cell-free supernatant protects HaCaT cells from UVB irradiation-induced photodamage and improves skin barrier function

Ultraviolet B (UVB) radiation is a major environmental stressor that induces oxidative stress, inflammation, and skin barrier dysfunction. Although Staphylococcus epidermidis ( S. epidermidis ) is a beneficial skin commensal, current evidence on its protective effects against UVB-induced skin damage has primarily focused on reference strains or a limited number of individual metabolites. The broader photoprotective potential of postbiotics derived from newly isolated skin commensal strains remains insufficiently characterized. Here, we investigated the anti-photodamage activity and underlying mechanisms of the cell-free supernatant of S. epidermidis CCSM0287 (SE 287-CFS), a multifunctional skin commensal isolated from healthy skin, in UVB-induced HaCaT cells. SE 287-CFS significantly reduced intracellular reactive oxygen species (ROS), malondialdehyde (MDA), and pro-inflammatory cytokines, while enhancing antioxidant enzyme activity and interleukin-10 (IL-10) secretion. Mechanistically, SE 287-CFS inhibited p65 nuclear translocation and suppressed activation of the ROS/MAPK/NF-κB signaling pathway. In addition, SE 287-CFS increased transepithelial electrical resistance (TEER) and promoted keratinocyte proliferation and migration, indicating improved skin barrier function. Non-targeted metabolomics combined with correlation analysis suggested that butyric and adipic acids were primarily associated with antioxidative and anti-inflammatory effects. Other organic acids, including succinic, acetic, and propanoic acids, may contribute to skin barrier repair. Together, this study demonstrates that SE 287-CFS protects against UVB-induced photodamage by modulating oxidative stress, suppressing inflammation, and improving skin barrier function. It also highlights the potential of postbiotics derived from skin commensals as candidates for microbiome-based skin photoprotection. IMPORTANCE Staphylococcus epidermidis is a dominant commensal skin bacterium that plays a crucial role in maintaining skin homeostasis and defending against various external stressors. UV radiation is a primary environmental factor that induces oxidative stress and inflammatory responses, resulting in photodamage and impaired skin barrier function. This study demonstrated the significant protective effect of SE 287-CFS in counteracting ultraviolet B (UVB)-induced skin damage. By modulating the reactive oxygen species (ROS)/MAPK/NF-κB signaling pathways, SE 287-CFS effectively alleviated oxidative stress, reduced inflammatory cytokine production, and enhanced skin barrier function. This research highlighted the potential of using skin commensal bacteria as a novel therapeutic strategy to enhance skin protection against UVB-induced damage, providing a promising approach to improve skin health under environmental stressors like UV radiation.