The Antibacterial Effect of Visible Blue Light on Biofilm Growth in vitro Model

Objectives: Previous studies showed that blue light, commonly used in restorative dentistry, induced a significant phototoxic effect on periopathogens and caused a reduction in VSC-producing bacteria in saliva and biofilm. Our aim is to determine the effect of blue light on the composition of different populations of the oral microbiota in an in vitro biofilm model.
Methods: Oral microbiota from whole saliva of 6 healthy volunteers were grown on hydroxyapatite discs in 96 wells plate to form biofilms, for 48h under anaerobic conditions at 37oC. The biofilms were exposed to blue light (wavelengths, 400-500nm) for 1 and 4 min (equivalent to fluences of 37 and 148 J/cm2, respectively), while non- exposed biofilms served as control. Half of the biofilm samples were examined immediately after exposure to light, and the other half had been grown anaerobically for 24h after their exposure, and then were similarly examined. All samples were assessed for bacterial viability: (i) using sonication and then viable counts of the suspended bacteria plated on blood agar and on differential agar for VSC-producing bacteria, and (ii) under the confocal laser scanning microscopy (CLSM) using live/dead staining.
Results: After exposure to light a significant decrease in the total amount of viable bacteria and VSC-producing bacteria was found (p<0.05, ANOVA), which was positively correlated with exposure time. While the total amount of bacteria in biofilm was less affected by the light 24h after exposure, a sustained reduction in the VSC-producing bacteria was obtained (p<0.05, ANOVA). CSLM results showed higher ratio of dead/live bacteria in biofilms immediately after their exposure to light, and when longer exposure time was used. Light influenced the viability of the bacteria through all the depth of the biofilm.
Conclusions: Blue light demonstrated enhanced antibacterial effect on the population of the VSC-producing bacteria in biofilm. This effect was sustained for at least 24h after exposure to light. We suggest the blue light as a non-conventional antimicrobial treatment that may shift the oral microbiota in biofilm towards a less pathogenic periodontal population.