Objectives: The increased occurrence of antibiotic resistance in general necessitates development of alternative antimicrobial drugs or methods. Further, certain cases of periodontitis respond poorly to conventional treatment. The principle of photodynamic therapy, currently used against certain cancers, may be a practical treatment modality for oral infections, presumably with low possibility for development of resistance. The treatment requires the presence of light-absorbing molecules (photosensitizer; PS) and irradiation with a light source emission that spectrally matches the light-absorption of the PS. The resulting reactive oxygen species and/or photoproducts formed may be toxic to cells and organisms. PS often requires pharmaceutical formulations to improve water solubility and hydrolytic- and photochemical stability, to avoid formation of aggregates and to control the drug release at the target.

Methods: Phototoxicity induced by the food-colourant curcumin (E100) as a PS in combination with blue light (fluorescent tubes; emission max.: 450 nm) on Gram-positive (G+) and –negative (G-) planktonic bacteria and biofilms. Formulations were single vehicles, such as micelles, surfactants, liposomes or cyclodextrines and complex foams consisting of one or more of the vehicles above.

Results and Conclusions: The degree of phototoxicity of curcumin (measured as number of colony forming units/ml) was dependent on the type(s) and concentration of formulations as well as curcumin concentration and light dose. Generally, G- bacteria and biofilms were less sensitive to the treatment than were G+. A six log reduction of G+ bacteria was obtained after treatment with several of the investigated formulated preparations containing 2.5 µM curcumin irradiated with 0.5 J/cm² blue light. To obtain the same reduction for G- bacteria a micelle/curcumin preparation of 25 µM curcumin irradiated with 30 J/cm² was required. Improved formulations with increased release of curcumin are under development.

Antimicrobial photodynamic treatment of oral infections
Bruzell E, Hegge AB, Tønnesen HH.
22nd European Dental Materials Conference, Birmingham, England, 29-30 Aug, 2013 (A)