Phototherapy of Pseudomonas aeruginosa -Infected Wounds: Preclinical Evaluation of Antimicrobial Blue Light (450-460 nm) Using In Vitro Assays and a Human Wound Skin Model.

Objective: To determine effective treatment strategies against bacterial infections of burn wounds with Pseudomonas aeruginosa , we tested different treatment regimens with antibacterial blue light (BL). Background: Infections of burn wounds are serious complications and require effective and pathogen-specific therapy. Hereby, infections caused by P. aeruginosa pose a particular challenge in clinical practice due to its resistance to many antibiotics and topical antiseptics. Methods: LED-based light sources (450-460 nm) with different intensities and treatment times were used. Antibacterial effects against P. aeruginosa were determined by colony-forming unit (CFU) assays, human skin wound models, and fluorescence imaging. Results: In suspension assays, BL (2 h, 40 mW/cm ² , 288 J/cm ² ) reduced bacterial number (>5 log ₁₀ CFU/mL). Applying 144 J/cm ² , using 40 mW/cm ² for 1 h was more effective (>4 log ₁₀ CFU) than using 20 mW/cm ² for 2 h (>1.5 log ₁₀ CFU). BL with low irradiance (24 h, 3.5 mW/cm ² , 300 J/cm ² ) only revealed bacterial reduction in thin bacteria-containing medium layers. In infected in vitro skin wounds only BL irradiation (2 h, 40 mW/cm ² , 288 J/cm ² ) exerted a significant antimicrobial efficacy (2.94 log ₁₀ CFU/mL). Conclusions: BL treatment may be an effective therapy for P. aeruginosa -infected wounds to avoid radical surgical debridement. However, a significant antibacterial efficacy can only be achieved with higher irradiances and longer treatment times (min. 40 mW/cm ² ; >1 h), which cannot be easily integrated into regular clinical treatment protocols, for example, during a dressing change. Further studies are necessary to establish BL therapy for infected burns among tissue compatibility and interactions with previous therapeutic agents.