Auswirkung einer wiederholten Photobiomodulation (405 nm Low-Level-Laser) auf das Wachstumsverhalten wundinfektionsrelevanter Mikroorganismen in Flüssignährmedien

: Eine in-vitro Studie

Abstract

Background:
Antimicrobial resistance is a global threat and urgently requires alternative treatment strategies. Healthcare-associated infections are particularly relevant in this context, with surgical-site infections being among the most common. Light-based methods, such as photobiomodulation with 405 nm, offer a promising non-antibiotic treatment option. The aim of this in-vitro study was to investigate the effect of repeated photobiomodulation with a 405 nm low-level-laser on the growth of selected wound infection-relevant bacteria in liquid culture medium.
Methods:
Five ATCC® reference strains (Enterococcus faecalis, Escherichia coli, Methicillin-resistant Staphylococcus aureus [MRSA], Pseudomonas aeruginosa, Staphylococcus aureus) were examined in Tryptic Soy Broth. Bacterial growth was measured using an absorption spectrometer by measuring the optical density at 600 nm (OD600). Irradiation was performed six times at twelve-hour intervals using a 405 nm low-level-laser (9 J/cm2 per cycle). For quantitative evaluation, the area under the growth curve (AUC) was calculated from the OD600-measurements and the time points at which defined OD600-thresholds were reached were determined.
Results:
The photobiological effect varied depending on the strain. Escherichia coli and MRSA showed significant AUC reductions (p < 0.05). While Escherichia coli exhibited delayed growth dynamics from stage_4 onwards, MRSA responded after the first irradiation (stage_1). Pseudomonas aeruginosa showed a clear but non-significant inhibitory trend. Enterococcus faecalis and Staphylococcus aureus did not respond significantly under the given conditions.
Conclusion and Discussion:
The results confirm and expand the existing research on the antimicrobial effect of light at 405 nm and underscore the potential of photobiomodulation as a selective, pathogen-specific, and tissue-sparing strategy against wound infection-relevant microorganisms – regardless of their resistance status. A comparison with the literature shows that the underlying photobiological mechanisms, are still poorly understood. This indicates a clear need for further research into mechanisms of action, standardized application protocols, and clinical transferability.

Date of Award	2025
Original language	German (Austria)
Awarding Institution	FH Gesundheitsberufe OÖ GmbH
Supervisor	Andreas Heltschl (Supervisor) & Manuel Holzer (Supervisor)