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Impaired wound healing and infections present a major concern for our health systems. Combined with the steady increase of antibiotic resistances and lack of new antibiotic drugs,
there is a pressing need for alternative treatment options, such as antimicrobial light-based therapies. While the germicidal properties of UV light have already been used for a long time, its negative side effects, for example DNA damage, photoaging and carcinogenicity, limit the possibilities and potential fields of application. Alternatively, blue light with wavelengths between 400 – 500 nm has shown promising results regarding the inactivation of a variety of microorganisms such as bacteria, yeasts and fungi viruses with the additive potential to improve wound healing (1). While the underlying mechanisms of blue light therapy have not been completely resolved yet, it has been proposed, that intrinsic chromophores e.g. porphyrins or flavins, generate ROS upon irradiation which destroy lipids, proteins and nucleic acids.
The aim of this study was to investigate the effects of LED devices emitting “soft” blue light with wavelengths > 430nm (provided by Repuls, Vienna, Austria) on the inactivation of gram-negative as well as gram-positive bacterial strains. It was revealed that the susceptibility towards the treatment differed greatly, presumably associated with the gene recA. In most bacterial strains, the protein RecA is responsible for homologous recombination, DNA repair and induction of the SOS response. Therefore, we hypothesized that the inactivation of the protein would increase the susceptibility of resistant strains and enhance the antimicrobial effects of the treatment. Although the potentiation of the therapy via RecA inhibitors was only partially successful, the influence of recA was confirmed by rescuing susceptible bacterial strains with the insertion of a plasmid carrying the gene. However, further experiments are needed to uncover the mechanisms behind the tolerability of blue light therapy and the importance of the SOS response. Nonetheless, progress was made towards a better understanding of the antibacterial actions of blue light. The modulation of the bacterial SOS response would not only benefit aBL therapy, but also antibacterial drug treatments, which are still the standard protocol for the care of infected wounds. Creating synergistic effects by combining these therapies into one singular treatment would likely increase therapeutic efficacy and is therefore a promising strategy to overcome the dilemma of antibiotic resistance.
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