In Vitro Bactericidal Effects of 625, 525, and 425 nm Wavelength (Red, Green, and Blue) Light-Emitting Diode Irradiation

Objective: The purpose of this study was to evaluate the relationship of 625, 525, and 425 nm wavelengths, providing average power output and effects on three common pathogenic bacteria. Background data: Ultraviolet (UV) light kills bacteria, but the bactericidal effects of UV may not be unique, as 425nm produces a similar effect. The bactericidal effects of light-emitting diode (LED) wavelengths such as 625 and 525nm have not been described. Before conducting clinical trials, the appropriate wavelength with reasonable dose and exposure time should be established. Materials and methods: The bactericidal effects of 625, 525, and 425nm wavelength LED irradiation were investigated in vitro for the anaerobic bacterium Porphyromonas gingivalis and two aerobes (Staphylococcus aureus and Escherichia coli DH5). Average power output was 6mW/cm(2) for 1h. The bacteria were exposed to LED irradiation for 1, 2, 4, and 8h (21.6, 43.2, 86.4, and 172.8J/cm(2), respectively). LED irradiation was performed during growth on agar and in broth. Control bacteria were incubated without LED irradiation. Bacterial growth was expressed in colony-forming units (CFU) and at an optical density at 600nm in agar and broth. Results: The bactericidal effect of LED phototherapy depended upon wavelength, power density, bacterial viable number, and bacteria species. The bactericidal effect of 425 and 525nm irradiation varied depending upon the bacterial inoculation, compared with unirradiated samples and samples irradiated with red light. Especially, P. gingivalis and E. coli DH5 were killed by 425nm, and S. aureus growth was inhibited by 525nm. However, the wavelength of 625nm was not bactericidal for P. gingivalis, E. coli DH5, or S. aureus. Conclusions: Irradiation at 625nm light was not bactericidal to S. aureus, E. coli, and P. gingivalis, whereas wavelengths of 425 and 525nm had bactericidal effects. S. aureus was also killed at 525nm.