Antimicrobial effects of repeated 405 nm low-level-laser photobiomodulation: an In-vitro study on surgical wound...

Antimicrobial resistance represents a major global health threat, requiring alternative non-antibiotic strategies. Light-based methods, particularly photobiomodulation (PBM) with 405 nm, have shown promise against clinically relevant pathogens. This in-vitro study investigated the effect of repeated PBM using a 405 nm low-level laser on the growth dynamics of wound infection-related bacteria. Five ATCC reference strains (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Methicillin-Resistant Staphylococcus aureus [MRSA] and Pseudomonas aeruginosa) were cultured in tryptic soy broth and subjected to six irradiation cycles at 12-hour intervals (9 J/cm² per cycle, 45 mW). Bacterial growth was monitored via optical density at 600 nm (OD₆₀₀). Quantitative analysis included calculation of the area under the growth curve (AUC) and determination of threshold times for OD₆₀₀ values between 0.1 and 0.5. Strain-specific effects were observed. Escherichia coli and MRSA exhibited significant AUC reductions compared to controls (p < 0.05); with MRSA responding after the first irradiation and Escherichia coli showing delayed effects from Stage_4 onwards. Pseudomonas aeruginosa showed a non-significant inhibitory trend, while Enterococcus faecalis and Staphylococcus aureus did not demonstrate significant differences. Repeated PBM with 405 nm selectively inhibited the growth of certain pathogens, underscoring its potential as a strain-specific, non-antibiotic strategy against wound infection-related bacteria. The results indicate a clear need for further research into mechanisms of action, standardized application protocols, and clinical transferability.