In recent studies, we showed that pulsed blue light is more potent in suppressing bacterial growth than continuous wave blue light. The potency of pulsed blue light makes it a viable antimicrobial for suppressing bacteria growth in biofilms, where the protective cover of the biofilm makes it is tougher to suppress bacteria. Consequently, we studied the efficacy of pulsed 450 nm light in suppressing the growth of MRSA and P. acnes biofilms. The results showed 100% bacterial suppression in planktonic cultures of MRSA irradiated with 7.6 J/cm2 three times a day, using 3 mW/cm2 irradiance, and in P. acnes planktonic cultures irradiated with 5 J/cm2 thrice daily for 3 days, using 2 mW/cm2 irradiance. However, a similar 100% suppression was not attained in MRSA or P. acnes biofilms irradiated thrice daily for 3 days at various fluences; but LIVE/DEAD assay showed a degree of bacterial suppression, with more live cells in controls than irradiated biofilms, and more dead cells in irradiated than control biofilms. In addition, while control biofilms had intact biofilm networks, irradiated biofilms had disrupted biofilm. The higher the dose, the more bacterial suppression and biofilm disruption. These findings confirm our previous reports that 100% bacterial suppression is attainable with pulsed blue light, and suggests further modification of the treatment protocol in order to achieve 100% bacterial suppression in biofilms.
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.