Optimizing the bactericidal effect of pulsed blue light: A correlative fluorescence spectroscopy study

The dosage and treatment schedules using blue light therapy in the treatment of P.acnes have not been optimized leading to less than satisfactory results and patient compliance. Our team has been developing optimized protocols using pulsed blue light with a novel wearable flexible printed LED substrate to suppress P.acnes bacterial growth. Aim: To optimize antimicrobial protocols using 450 nm pulsed light against P. acnes and correlate optimal bacterial suppression with fluorescence intensity of bacterial absorbing pigments. Methods: Printed 450 nm light substrates in 33% pulsed mode and irradiance of 2 mW/cm², at various time points were used. The protocol involved multiple exposures (0, 3, and 6 hours) of 450 nm, pulsed 33% at an irradiance of 2 mW/cm². The change in fluorescence intensity was evaluated after irradiation with 5, 3.6 and 3 J/cm² on days one, two and three; 5 and 3.6 J/cm² on day four and 5 J/cm² on day five. Spectroscopic data, digital images and percent survival were obtained. Results: Optimal bacterial suppression of 100% was obtained using the protocol. Spectroscopic data correlated with the three-hour time interval frame, before the next exposure. The protocol involved a sequential reduction in fluence over a five-day period, correlating with the "depletion and replenishment" of fluorescence intensities of the excited photosensitizers in P. acnes. Conclusion: Both bacterial survival and fluorescence intensity data supports our hypothesis that irradiation of P. acnes three-hours interval produces maximum bacterial suppression. This optimization advances our knowledge towards the use of this protocol in clinical settings.