Characterization of Blue Light Treatment for Infected Wounds: Antibacterial Efficacy of 420, 455, and 480 nm Light-Emitting Diode Arrays Against Common Skin Pathogens Versus Blue Light-Induced Skin Cell Toxicity

Abstract

Objective: To determine effective treatment strategies against bacterial infections of chronic wounds, we tested different blue light (BL)-emitting light-emitting diode arrays (420, 455, and 480 nm) against wound pathogens and investigated in parallel BL-induced toxic effects on human dermal fibroblasts. Background: Wound infection is a major factor for delayed healing. Infections with Pseudomonas aeruginosa and Staphylococcus aureus are clinically relevant caused by their ability of biofilm formation and their quickly growing antibiotics resistance. BL has demonstrated antimicrobial properties against various microbes. Methods: Determination of antibacterial and cell toxic effects by colony-forming units (CFUs)/biofilm/cell viability assays, and live cell imaging. Results: A single BL irradiation (180 J/cm²), of P. aeruginosa at both 420 and 455 nm resulted in a bacterial reduction (>5 log₁₀ CFU), whereas 480 nm revealed subantimicrobial effects (2 log₁₀). All tested wavelengths of BL also revealed bacteria reducing effects on Staphylococcus epidermidis and Escherichia coli (maximum 1-2 log₁₀ CFU) but not on S. aureus. Dealing with biofilms, all wavelengths using 180 J/cm² were able to reduce significantly the number of P. aeruginosa, E. coli, and S. epidermidis. Here, BL_420nm achieved reductions up to 99%, whereas BL_455nm and BL_480nm were less effective (60-83%). Biofilm-growing S. aureus was more BL sensitive than in the planktonic phase showing a reduction by 63-75%. A significant number of cell toxic events (>40%) could be found after applying doses (>30 J/cm²) of BL_420nm. BL_455nm showed only slight cell toxicity (180 J/cm²), whereas BL_480nm was nontoxic at any dose. Conclusions: BL treatment can be effective against bacterial infections of chronic wounds. Nevertheless, using longer wavelengths >455 nm should be preferred to avoid possible toxic effects on skin and skin cells. To establish BL therapy for infected chronic wounds, further studies concerning biofilm formation and tissue compatibility are necessary.

Keywords: antimicrobial efficacy; blue light; cell toxicity; violet light; wound infection.