BACKGROUND: Oxygen is generally considered essential for lethal 
photosensitisation by photodynamic processes. The oral anaerobes, Prevotella 
intermedia and P. nigrescens are known to be photosensitive, but are also 
extremely sensitive to the cytotoxic effects of oxygen.
METHODS: The Prevotellaceae were exposed to two 405 nm light sources for 
different exposure times in an anaerobic chamber. Viable counts of the light 
exposed samples were compared to light-free controls to determine the proportion 
of bacteria killed.
RESULTS: Lethal photosensitivity was demonstrated against P. intermedia and P. 
nigrescens. The proportions of bacteria killed by either the light-emitting 
diode or laser pointer were similar at a given energy density (J/cm(2)).
CONCLUSIONS: Lethal photosensitivity was demonstrated in two species of 
Prevotella under anaerobic conditions.