Objectives: To explore- 1)The effects of exposure to non-coherent visible light (wavelengths, 400-500 nm) on the expression of different genes related with the formation of biofilm by
S.mutans. 2)The bactericidal effects of combining such visible light with commonly used antibacterial agents and its mechanism. Methods:
S.mutans biofilm was constructed in a medium supplemented with sucrose. Samples were exposed to a visible-light source for 60 to 600sec (equivalent to 68-686J/cm2). Total RNA from
S.mutans in biofilm, exposed to visible-light, was extracted and used to create cDNA. The expression of genes specifically associated with biofilm formation was measured using real time RT-PCR. All samples were normalized using 16s-rRNA and compared to the non-exposed control sample. Samples were exposed to visible-light for 30 and 60sec (34 and 68J/cm2 respectively) with and without antibacterial agents (CPC or H2O2). Samples were exposed to light for 10min (686J/cm2) in the presence of reactive oxygen species (ROS) scavenger. The biofilm was dissociated using a probe-sonicator. The number of colony forming units of each sample was compared to the non-exposed control in order to asses the antibacterial effect. Results: Up-regulation, in several genes involved with biofilm formation (
gtfB,
gtfC,
ftf,comDE,
brp) was observed following exposure to light. Such effect proved to be dose-dependent. The combination of sub-MIC concentrations of H2O2, along with all tested time exposures, showed a synergistic antibacterial effect; whereas, combining CPC with light demonstrated no synergism. Scavengers caused a significant reduction in the bactericidal effect. Conclusion: Results show that the visible-light at a non-lethal dose has a genomic influence on
S.mutans genes, associated with biofilm formation, which is dose-dependent and passed to future generations. Visible light affected
S.mutans by ROS generation which could explain the synergistic effect between the visible light and H2O2.
Supported in part by the Mutual Grant of the Hebrew University-Hadassah.