title: Repeated exposures to blue light-activated eosin Y enhance inactivation of E. faecalis biofilms, in vitro.
abstract: BACKGROUND
  In dentistry, antibacterial photodynamic therapy (a-PDT) has shown promising results for inactivating bacterial biofilms causing carious, endodontic and periodontal diseases. In the current study, we assessed the ability of eosin Y exposed to 3 irradiation protocols at inactivating Enterococcus faecalis biofilms, in vitro.
  
  
  METHODS
  E. faecalis biofilms formed on hydroxyapatite disks were incubated with eosin Y (10-80μM), then activated with blue light using different irradiation protocols. Biofilms exposed to continuous exposure were incubated for 40min before being light-activated for 960 s. For the intermittent exposure, biofilms were exposed 4 times to the light/photosensitizer combination (960 s total) without renewing the photosensitizer. For repeated a-PDT, the same light dose was delivered in a series of 4 irradiation periods separated by dark periods; fresh photosensitizer was added between each light irradiation. After treatment, bacteria were immediately labeled with LIVE/DEAD BacLight Bacterial Viability kit and viability was assessed by flow cytometry (FCM). Results were statistically analyzed using one-way ANOVA and Tukey multiple comparison intervals (α=0.05).
  
  
  RESULTS
  The viability of E. faecalis biofilms exposed to 10μM 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 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.
  
  
  CONCLUSIONS
  The results of this study indicate that blue light-activated eosin Y can photoinactivate E. faecalis biofilms grown on hydroxyapatite disks. Also, repeated exposures to blue light-activated eosin Y were shown to significantly improve efficacy. Further studies seem warranted to optimize the antibacterial activity of blue light-activated eosin Y on major oral pathogens.
authors.affiliation: Endodontics Unit, Section of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Karlo
authors.initials: K
authors.lastname: Marinic
authors.affiliation: Endodontics Unit, Section of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Manoil
authors.affiliation: Endodontics Unit, Section of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Anna
authors.initials: A
authors.lastname: Filieri
authors.affiliation: Department of Restorative Dentistry, University of Washington, Seattle, WA, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Wataha
authors.affiliation: Service of Infectious Diseases, University Hospitals of Geneva, University of Geneva, Geneva, Switzerland.
authors.forename: Jacques
authors.initials: J
authors.lastname: Schrenzel
authors.affiliation: Department of Pharmaceutics and Biopharmaceutics, School of Pharmaceutical Sciences, University of Geneva, Switzerland.
authors.forename: Norbert
authors.initials: N
authors.lastname: Lange
authors.affiliation: Endodontics Unit, Section of Dental Medicine, University of Geneva, Geneva, Switzerland. Electronic address: Serge.Bouillaguet@unige.ch.
authors.forename: Serge
authors.initials: S
authors.lastname: Bouillaguet
mesh_terms: D018441:Biofilms; D017886:Durapatite; D013293:Enterococcus faecalis / Q000187:drug effects*; D004801:Eosine Yellowish-(YS) / Q000494:pharmacology*; D006801:Humans; D050296:Microbial Viability / Q000187:drug effects; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*
chemical_list: D017319:Photosensitizing Agents; D017886:Durapatite; D004801:Eosine Yellowish-(YS)