Method: Enterococcus faecalis were cultured onto Columbia agar plates, transferred into culture medium (BHI, Oxoid, CH) and then cultured for 48h on hydroxyapatite disks (Clarkson Chromatography) to allow biofilm formation. Biofilms were then incubated for 10 minutes in presence of 10 µM eosin Y prior to light activation for 240 s using an Optilux 501 light-curing unit (Kerr-Hawe, Bioggio, Switzerland) emitting blue light (350-500 nm). Specimens were either exposed to 1, 2, 3 or 4 repetitions of light/chemical combination. After each irradiation, 0.2 ml of bacterial suspension was collected for viability measurement using the LIVE/DEAD BacLight Bacterial Viability kit (Life technologies, Zug, CH). Bacterial viability was assessed by flow cytometry (Accuri C6). 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: The viability of E. faecalis biofilms exposed to 10 µM eosin Y was significantly reduced compared to controls (light only- eosin Y only). After a second exposure to blue light-activated eosin Y, viability significantly decreased from 58% to 12% whereas only 6.5% of the bacterial biofilm remained live after a third exposure (p < 0.05). Only 3.5% of the bacterial population survived after the fourth exposure.
Conclusion: The current study demonstrates the possible utility of blue-light activated eosin Y as a disinfecting agent. Repeated exposures of bacterial biofilms to blue-light activated eosin Y significantly improved antimicrobial activity