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

Abstract 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/cm 2 per cycle, 45 mW). Bacterial growth was monitored via optical density at 600 nm (OD 600 ). Quantitative analysis included calculation of the area under the growth curve (AUC) and determination of threshold times for OD 600 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.