The Differential Effect of Blue Light on Oral Microbiota From Healthy and Periodontal Diseased Patients

Objectives: Previous studies showed that blue light, induces a phototoxic effect on periopathogens and causes a significant decrease in the total amount of viable bacteria in in vitro biofilm models using oral microbiota from whole saliva of healthy volunteers. Our aim is to compare blue light effect on the composition of oral microbiota in a biofilm model from healthy volunteers and periodontitis patients.
Methods: Oral microbiota from whole saliva of 6 healthy volunteers and periodontitis patients were grown on hydroxylapatite discs in 96wells plate to form biofilms for 48h under anaerobic conditions at 37°^C. The biofilms were exposed to blue light (wavelengths, 400-500nm) for 1and 4min (equivalent to fluencies of 37and 148J/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 were allowed to be grown anaerobically for 24h after their exposure, and then were similarly examined. All samples were assessed for bacterial viability on blood agar and on differential agar for volatile sulfide compounds (VSC) producing bacteria, and 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 in samples of the healthy, which was positively correlated with exposure time. While in samples of periodontal diseased, the reduction was found in the VSC-producing bacteria viable counts. 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 in both groups. CSLM results showed higher ratio of dead/live bacteria in biofilms immediately after their exposure to light, and when longer exposure time was used in both groups. Light influenced the viability of bacteria through all the depth of biofilm. The effect of blue light on bacteria from periodontitis patients were more significant compared to healthy.
Conclusions: There is a deferential effect of blue light on oral microbiome; mainly affect the periopathogens while allows other types to survive. This suggests making a shift in the biofilm consistence towards the nonpathogenic bacteria in healthy, and in diseased patients.