title: In vitro bactericidal effects of 625, 525, and 425 nm wavelength (red, green, and blue) light-emitting diode irradiation.
abstract: 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
  Ultraviolet (UV) light kills bacteria, but the bactericidal effects of UV may not be unique, as 425 nm produces a similar effect. The bactericidal effects of light-emitting diode (LED) wavelengths such as 625 and 525 nm have not been described. Before conducting clinical trials, the appropriate wavelength with reasonable dose and exposure time should be established.
  
  
  METHODS
  The bactericidal effects of 625, 525, and 425 nm wavelength LED irradiation were investigated in vitro for the anaerobic bacterium Porphyromonas gingivalis and two aerobes (Staphylococcus aureus and Escherichia coli DH5α). Average power output was 6 mW/cm(2) for 1 h. The bacteria were exposed to LED irradiation for 1, 2, 4, and 8 h (21.6, 43.2, 86.4, and 172.8 J/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 600 nm 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 525 nm irradiation varied depending upon the bacterial inoculation, compared with unirradiated samples and samples irradiated with red light. Especially, P. gingivalis and E. coli DH5α were killed by 425 nm, and S. aureus growth was inhibited by 525 nm. However, the wavelength of 625 nm was not bactericidal for P. gingivalis, E. coli DH5α, or S. aureus.
  
  
  CONCLUSIONS
  Irradiation at 625 nm light was not bactericidal to S. aureus, E. coli, and P. gingivalis, whereas wavelengths of 425 and 525 nm had bactericidal effects. S. aureus was also killed at 525 nm.
authors.affiliation: 1 Department of Oral Pathology, Medical Research Center for Biomineralization Disorders, School of Dentistry, Dental Science Research Institute, Chonnam National University , Bug-Gu, Gwangju, Republic of Korea.
authors.forename: SangWoo
authors.initials: S
authors.lastname: Kim
authors.forename: Jisun
authors.initials: J
authors.lastname: Kim
authors.forename: WonBong
authors.initials: W
authors.lastname: Lim
authors.forename: SangMi
authors.initials: S
authors.lastname: Jeon
authors.forename: OkSu
authors.initials: O
authors.lastname: Kim
authors.forename: Jeong-Tae
authors.initials: JT
authors.lastname: Koh
authors.forename: Chang-Su
authors.initials: CS
authors.lastname: Kim
authors.forename: HongRan
authors.initials: H
authors.lastname: Choi
authors.forename: OkJoon
authors.initials: O
authors.lastname: Kim
mesh_terms: D015169:Colony Count, Microbial; D003116:Color; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000528:radiation effects*; D010789:Phototherapy / Q000295:instrumentation / Q000379:methods*; D016966:Porphyromonas gingivalis / Q000528:radiation effects*; D013211:Staphylococcus aureus / Q000528:radiation effects*