Antimicrobial blue light-bathing therapy for wound infection control

Introduction: The prevalence of antibiotic resistance and tolerance in wound infection management poses a serious and growing health threat, necessitating the exploration of alternative approaches. Antimicrobial blue light therapy has been rigorously explored as an appealing alternative, offering the advantages of a non-pharmacological approach, broad-spectrum efficacy, and no reported resistance. However, its successful clinical adoption has been hampered by the requirement for high irradiance levels, which particularly raises safety concerns. Here, we introduce a light-bathing strategy that employs prolonged, continuous exposure to blue light at an irradiance range lower by more than an order of magnitude (5 mW/cm2) for safe and effective wound infection control.

Materials and

Methods: We established the blue light-bathing strategy based upon consistent in vitro observations of bacteriostatic effects of blue light at low irradiance range for various bacterial species or strains (S. aureus, P. aeruginosa, E. coli), where the minimum irradiance to enable complete growth inhibition was defined as its minimum inhibitory irradiance (MII). To test the light-bathing strategy on live animals, we devised wearable wound patches equipped with 410 nm blue light emitting diodes and engineered a tethered prototype optimized for use with freely moving rat models. Our in vivo phototoxicity study was performed on rat dorsal regions either for healthy skin or abrasion wound at various bathing irradiances over 2-day treatment course. We monitored skin reactions and performed H&E and TUNEL histopathology to comprehensively evaluate skin damage or side effects on wound healing to determine maximum permissible irradiance (MPI). We then evaluated the bathing regimen at MPI on rat models of wound infection induced by clinical antibiotic-resistant S. aureus or P. aeruginosa strains. Its antimicrobial efficacy was rigorously confirmed through various methods, including clinical wound signs, immunohistochemical analysis of key cytokine markers, bioluminescence imaging of bacterial bioburden, fluorescence in situ hybridization imaging of specie-specific bacterial distribution, and endpoint colony-forming unit enumeration of bacterial load from wound biopsies.

Results, Conclusions, and Discussions: Our work represents a substantial progress in antimicrobial blue light therapy by introducing a novel blue light-bathing therapy that diverges from the high irradiance-based traditional protocols (Fig. 1a-f). We established its biosafety, antimicrobial efficacy, and translational feasibility via extensive in vivo studies utilizing custom-built wearable light-emitting patches on rat models of wound infection (Fig. 1g). We discovered that prolonged, continuous exposure to blue light at low irradiance (just 5 mW/cm2) can effectively prevent bacterial growth and keep the in vivo wound bioburden low for two most common antibiotic-resistant wound pathogens, S. aureus and P. aeruginosa, all while minimizing photothermal risks (Fig. 2 showcasing P. aeruginosa-induced infection). We further delineated a therapeutical window for the light-bathing therapy that is bounded by MII at 2 mW/cm2 level and MPI at 10 mW/cm2 level. Our findings highlight the potential of blue light-bathing as a new antimicrobial strategy in wound care.

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