Parameter optimization and mechanism of action of Light‑Emitting Diode phototherapy in a rat model of bacterial vaginosis

Objective To investigate the antibacterial effects of LED phototherapy on Gardnerella vaginalis ( Gv ) and Escherichia coli ( E. coli ), optimize key irradiation conditions for LED phototherapy by establishing an in vivo infection model, and evaluate its feasibility for treating bacterial vaginosis. Methods Bacterial colonies were irradiated with LEDs at different wavelengths (405 nm, 415 nm, 430 nm, 630 nm, 850 nm). Bacterial survival and morphology were assessed via colony counting, SYTO9/PI fluorescence staining, and scanning electron microscopy. Intracellular oxidative stress and antioxidant systems were quantitatively measured. Genomic DNA integrity was analyzed by agarose gel electrophoresis to validate the bactericidal mechanism. The effects on vaginal epithelial cell (VK2/E6E7). viability were assessed using CCK-8 assays, ROS detection, and SYTO9/PI live/dead staining. A rat model of bacterial vaginosis was established to optimize vaginal LED irradiation parameters, with inflammatory cell infiltration assessed by H&E staining, and expression levels of IL-1β and TNF-α in vaginal tissues evaluated by immunohistochemistry (IHC) with semi-quantitative image analysis. Results Among the tested wavelengths, 415 nm LED demonstrated optimal antibacterial efficacy. At 50 mW/cm² intensity for 30 min, it exhibited the most significant bactericidal effect against Gv and E. coli . This condition induced substantial ROS production in bacteria, inhibited SOD and CAT activity, leading to bacterial cell membrane damage and genomic DNA fragmentation. This irradiation condition exhibited no significant toxicity to vaginal epithelial cells VK2/E6E7. In a rat model, LED treatment under these conditions significantly improved vaginal inflammation symptoms and pathological histological findings, while reducing IL- 1β and TNF-α expression. Conclusion This study established the optimal LED irradiation conditions for BV-associated pathogens as 415 nm wavelength, 50 mW/cm² power, and 30 min exposure (irradiation dose 90 J/cm²). These conditions exert significant antibacterial effects against Gv and E. coli by inducing bacterial ROS production, while maintaining excellent cellular safety. In rat cell models, it simultaneously demonstrated anti-inflammatory and tissue repair potential in both bacterial and in vivo settings, offering a novel therapeutic strategy for the clinical management of bacterial vaginosis.