Lethal photosensitization of oral pathogens via a red-filtered halogen lamp

Abstract

Problem: We designed an in vitro experiment to achieve phototoxic results on 2 common oral pathogens, using a high intensity red-filtered halogen lamp (HL). Our goal was to determine the minimum duration of light exposure and drug dilution to achieve at least 50% reduction in bacteria counts. Methods: Porphyromonas gingivalis and prevotella intermedia were used in this experiment. The source for light energy was a continuously working, high intensity, red-filtered HL. The light was transmitted through a flexible light guide over petri dishes containing live bacteria. Microorganisms were exposed to halogen light for 5, 10, and 20 minutes. Methylene blue (MB) in concentrations of 0.1%, 0.075%, 0.05%, 0.025%, and 0.01% was used as a phosensitizing agent. Light energy alone and MB alone was used as controls. Results: Optimum lethal photosensitization (50% or more bacteria killing) of oral pathogens was achieved under the following conditions: (1) HL illumination for 5 minutes and longer with 0.05% MB; (2) exposure to light for 20 minutes in the presence of 0.025% and 0.01% MB. Light exposure for 20 minutes in the absence of MB was not effective in killing bacteria. In the absence of light, MB at concentrations of 0.025% and 0.001% was not effective. Reduction of bacteria with the use of 0.05% MB alone was also insignificant. However, 0.075% and 0.1% MB, even in the absence of light was found to be bacteriocidal. Conclusion: Our in vitro data indicate that we were able to achieve lethal photosensitization of 2 common oral pathogens with a high-intensity red-filtered HL in the presence of diluted MB. Significance: In this era of increased incidence of antibiotic resistance, bacterial killing with laser or light energy in the presence of photosensitizing agents can prove to be a valuable treatment modality. Support: Support from Otolaryngology Research and Education Foundation