Effects of Photodynamic Antimicrobial Chemotherapy on a Mature Oral Biofilm

Photodynamic antimicrobial chemotherapy (PACT) utilizes the combination of dyes and light sources to produce reactive oxygen species (ROS) aiming microorganism photokilling. It has the potential to be applied in the treatment and prevention of oral infectious diseases. Objectives: The aim of this present investigation was to verify the efficacy of curcumin, a natural compound used as photosensitizer, which is excited by the blue LED light, on a mature Streptococcus mutans biofilm. Methods: The treatments were performed using 2.5mM or 5mM of curcumin (C) excited by LED light (L) in the blue wavelength (400-450 nm) operated at different energy densities at several irradiation times. S. mutans UA159 biofilms were formed on saliva-coated hydroxyapatite discs in batch culture at 37^oC, 5%CO₂. Tryptone-yeast extract broth containing 1% sucrose was changed daily. After the 5^th day, the mature biofilm was treated: without C and L (C^-L^-, control); with C and without L (C⁺L^-); without C and with L (C^-L⁺) and with C and L (C⁺L⁺; PACT group). Morphological analyses and survival bacteria rate (CFU)/mg of biofilm dry weight were analyzed. Cytotoxicity test was performed using human keratinocyte cells. Results: Biofilm morphology changed after PACT exposure with a substancial photokilling reduction rate following a dose-response pattern.  There was no toxicity compared to the control. Conclusions: Curcumin is a natural, non-toxic photosensitizer has the potential photodynamic antimicrobial effect against a mature S. mutans oral biofilm.