Combining light exposure and hydrogen peroxide against Streptococcus mutans biofilm

Objectives: To explore the potential antibacterial synergistic effect between blue light (wavelengths, 400-500 nm) and hydrogen peroxide on Streptococcus mutans in biofilm. Methods: Streptococcus mutans were grown in a 96 well microplate containing BHI supplemented with 4% sucrose. After over night incubation at 370C (5% CO2), the bacteria were washed with PBS and different concentration of H2O2 (1%, 0.1%, 0.01%( was added to each well. Each sample was exposed to a plasma arc curing (PAC) light source for either 30 or 60 s, equivalent to fluences of ~ 31 and 62 J/cm2 respectively. After light exposure the samples were washed with PBS and 200 µl PBS were added to each sample. The biofilm was removed from the well by a probe sonicator. The samples were diluted and grown in mitis salivarius agar, containing bacitracin and tellorite at 370C (5% CO2) for 48 h, after which the colony forming units (CFU) were counted. The synergistic effect was assessed by a comparison between bacterial viability (CFU) of the samples (combined light and H2O2 treatment) and that of the control samples (light or H2O2 in separate treatment). Results:In all tested light dosages we found that using H2O2 in concentrations lower than the MIC, immediately followed by exposure to blue light, had an extensive bactericidal affect. Reduction in bacterial viability between 2-5 log was observed pending on the specific H2O2 and light combinations. Control samples, containing the same H2O2 concentrations or light exposure, showed no effect on bacterial growth. Conclusion:These results show a synergistic effect between blue light and H2O2. Further more the results suggest that this procedure has the capability to infiltrate in to the deep layers of the biofilm. Supported in part by a grant of the Israeli Ministry of Health.