白色LED照射による<i>Porphyromonas gingivalis</i>の殺菌効果

Abstract

Photodynamic therapy (PDT) is a medical treatment for cancers and infections with light irradiation and photosensitizers, which are excited by being exposed to light of a specific wavelength. Recently, PDT is applied to the treatment of periodontal disease. In this study, we investigated the bactericidal effect against Porphyromonas gingivalis, which is a periodontopathogenic bacteria, by white LED (light-emitting diode) irradiation with a higher visibility in the oral cavity. P. gingivalis (ATCC33277) was anaerobically cultured in brain-heart infusion (BHI) media, adjusted to an optical density of 0.3 using a photoelectrometer, and was then used as the bacterial solution for this experiment. After the bacterial solution was dispensed into a 96-well, clear, flat-bottom plate at 100 μL/well, the samples were irradiated with a white LED (irradiation intensities: 10, 20, 30 J/cm2, irradiation distance: 15 mm). The bacterial solutions were diluted and anaerobically cultured on blood agar at 37°C for 7 days. Then, the colony forming units (CFU) were counted and compared to that of the control group (LED non-irradiation) to determine the bactericidal effect. Irradiation with the white LED resulted in a statistically significant decrease in CFU, with the number of CFU decreasing as the irradiation intensity increased. In the second part of the study, we examined two photosensitizers: Protoporphyrin IX and Fluorescein, for use in PDT with white LED as a light source. The irradiation intensity of white LED was set at 20 J/cm2, and the concentration of each of the photosensitizers was set at 100 μM. A photosensitizer group (addition of the bacterial solution with photosensitizer and LED non-irradiation), an LED-irradiated group (bacterial solution alone and LED irradiation) and a combination group (addition of the bacterial solution with photosensitizer and LED irradiation) were compared to a control group (bacterial solution alone and LED non-irradiation), with the bactericidal effect evaluated by CFU measurements as described above. Neither of the photosensitizers affected the bactericidal effect. On the other hand, CFU of the combination group showed a statistically significant decrease compared to that of the LED-irradiated group. These results indicate that white LED irradiation has a bactericidal effect against P. gingivalis, and suggest that PDT with a combination of white LED irradiation and Protoporphyrin IX or Fluorescein added as a photosensitizer increase the bactericidal effect more than white LED irradiation alone.