title: Lethal photosensitization of Porphyromonas gingivalis by their endogenous porphyrins under anaerobic conditions: an in vitro study.
abstract: BACKGROUND
  Lethal photosensitization has been previously demonstrated in Porphyromonas gingivalis, but oxygen is considered to be essential to this process. However, since P. gingivalis is a periodontal pathogen which grows in the low oxygen conditions found in the subgingival crevice, it was considered prudent to study its photosensitivity in anaerobic conditions.
  
  
  METHODS
  A series of experiments were undertaken to attempt to induce lethal photosensitization in P. gingivalis (ATCC 33277) under strict anaerobic conditions using two different 405 nm light sources. Samples of P. gingivalis were grown on a blood-containing, solid growth medium before being suspended in saline and then exposed to 405 nm light delivered by either a hand-held light source (Toothcare™) (11.4 mW/cm(2)) or a laser pointer (328.5 mW/cm(2)). With the exception of the adjustment of the P. gingivalis suspensions to a fixed optical density, the experiments were carried out in their entirety within an anaerobic chamber.
  
  
  RESULTS
  The lowest Toothcare light dose tested (0.34 J/cm(2); 30s) yielded a statically significant kill of 63.4% which increased to 94.1% kill at higher light doses (3.42 J/cm(2); 300 s). The laser pointer similarly achieved kills of 90.2% at the lower light dose tested (9.86 J/cm(2); 30s) and 94.5% kill at the highest light dose (98.55 J/cm(2); 300 s).
  
  
  CONCLUSIONS
  Lethal photosensitization can be instigated in planktonic suspensions of P. gingivalis at 405 nm delivered by hand-held devices under anaerobic conditions. This suggests the possibility that lethal photosensitization occurred by the oxygen-independent type I pathway as oppose to the oxygen-dependent type II pathway.
authors.affiliation: Department of Health Services Research, University of Liverpool, Liverpool, UK; School of Dentistry, University of Liverpool, Liverpool, UK. Electronic address: chope@liv.ac.uk.
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Hope
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Hindley
authors.forename: Zeeshan
authors.initials: Z
authors.lastname: Khan
authors.forename: Elbert de Josselin
authors.initials: Ede J
authors.lastname: de Jong
authors.forename: Susan M
authors.initials: SM
authors.lastname: Higham
mesh_terms: D000693:Anaerobiosis / Q000502:physiology / Q000528:radiation effects; D017209:Apoptosis / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D008027:Light; D010100:Oxygen / Q000378:metabolism; D017319:Photosensitizing Agents / Q000378:metabolism; D011166:Porphyrins / Q000378:metabolism*; D016966:Porphyromonas gingivalis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects*; D011829:Radiation Dosage
chemical_list: D017319:Photosensitizing Agents; D011166:Porphyrins; D010100:Oxygen
keywords: Lethal photosensitization; Light; Photodynamic therapy; Porphyromonas gingivalis; Protoporphyrin IX