Method: Enterococcus faecalis were cultured onto Columbia agar plates, transferred into culture medium (BHI, Oxoid, CH) and then grown for 48h on hydroxyapatite disks (Clarkson Chromatography) to allow biofilm formation. Biofilms were then incubated for 10 minutes in presence of various concentrations of eosin Y (0-10-20-40-80-100 µM) prior to light activation for 240 s using an Optilux 501 light-curing unit emitting blue light (350-500 nm). After light irradiation, biofilms were sonicated 20 s and 0.2 ml of bacterial suspension was collected for viability measurement using LIVE/DEAD BacLight Bacterial Viability kit (Life technologies, Zug, CH). Bacterial viability was assessed by flow cytometry (Accuri C6, BD). Control groups received light or eosin Y only; the entire experiment was repeated 3 times (n=12). Results were statistically analyzed using a using one-way ANOVA and Tukey multiple comparison intervals (α = 0.05).
Result: Flow cytometric analysis of controls showed that 95 ± 4 % of cells were live, 3 ± 2 % were dead and 2 ± 1 % were injured. Concentrations of light-activated eosin-Y of 10 and 20 µM significantly reduced E. faecalis viability down to 73.5 ± 9.5 % and 70 ± 4.5 % respectively (p < 0.05). Also, the percentage of injured bacteria decreased in a dose dependent manner suggesting that injured cells are progressively dying. Higher concentrations (40-80-100 µM) did not induce any additional effect.
Conclusion: The current results support further exploration of blue light activated eosin Y as an antimicrobial agent for endodontic therapy.