Improvement of the antimicrobial efficacy of high-intensity blue light against Pseudomonas aeruginosa by discontinuous irradiation.

Wound infections caused by Pseudomonas aeruginosa (PA) are a common cause of death due to subsequent sepsis in immunosuppressed burn patients. Blue light at 455 nm exhibits antibacterial properties against PA and may offer a therapeutic option for treating such infections. However, low intensities require longer treatment durations, while high intensities cause temperature-related challenges. We therefore investigated the antibacterial efficacy of discontinuous blue light treatment (DBLT) at high intensity. DBLT cycles (up to 8) comprised 3 min of irradiation (300 mW/cm2) followed by a 2, 4, or 8 min pause to deliver the same doses (up to 432 J/cm2) as continuous blue light treatment (CLBT). In suspension assays, DBLT with 4-min pauses was most effective, achieving complete bacterial eradication after 5 cycles, whereas CLBT at the same dose (270 J/cm2) resulted in only a 1-log-level reduction. In a wound contamination model, DBLT (8 cycles, 4-min pauses) reduced bacterial load by 5 log levels, whereas CLBT only reduced it by 1-2 log levels. Flow cytometry and the redox-sensitive probe DCFH-DA assessed blue light-induced oxidative stress in PA. DBLT caused more oxidative stress (2-fold) than CLBT. This suggests that pauses in irradiation enhance the production of reactive species, which may accumulate and affect bacterial vitality. In conclusion, incorporating defined pause intervals into blue light therapy enhances antibacterial effectiveness, reduces heat development, and may improve clinical outcomes for bacterial infections in burn patients.