title: Ex vivo killing of Enterococcus faecalis and mixed plaque bacteria in planktonic and biofilm culture by modified photoactivated disinfection.
abstract: OBJECTIVE
  To compare the efficacy of conventional and modified photoactivated disinfection (PAD) against Enterococcus faecalis and mixed plaque bacteria in suspension and biofilms.
  
  
  METHODS
  Enterococcus faecalis (four strains) and mixed plaque bacteria from three adult volunteers were suspended in water, added to methylene blue (MB, 15 μmol L⁻¹), MB mixed with 0.5% hydrogen peroxide and 0.05% chlorhexidine (CHX), MB mixed with 0.5% hydrogen peroxide and 0.05% EDTA or MB mixed with 0.05% EDTA and 0.05% CHX and exposed to laser irradiation from 10 s to 5 min. After exposure, samples were taken, serially diluted and grown aerobically and anaerobically on Tryptic Soy Agar plates or on blood agar plates for 24 and 72 h, respectively. For biofilm experiments, E. faecalis and mixed plaque biofilms were grown on sterile hydroxyapatite (HA) discs coated overnight with bovine dermal collagen type I for 3 weeks. After exposure to MB or MB and low concentration of EDTA with either hydrogen peroxide or CHX, the percentage of killed bacteria by PAD was evaluated using viability staining and confocal laser scanning microscope. For statistical analysis, one-way analysis of variance was performed.
  
  
  RESULTS
  Conventional PAD killed from 90.76% to 100% E. faecalis for 3 min, but failed to kill all plaque bacteria even after 5 min of laser irradiation. In modified PAD, up to 100% of suspended E. faecalis and mixed plaque bacteria were killed after 1 min and 30 s of irradiation. Up to twenty times more biofilm bacteria were killed by modified PAD than by conventional PAD with 15 μmol L⁻¹ MB (P < 0.001) and up to eight times more than 2% CHX (P < 0.001) and 1% sodium hypochlorite (P < 0.001).
  
  
  CONCLUSIONS
  Modified PAD was superior to conventional PAD against planktonic and biofilm bacteria.
authors.affiliation: Division of Endodontics, Department of Oral Biological and Medical Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Stojicic
authors.forename: H
authors.initials: H
authors.lastname: Amorim
authors.forename: Y
authors.initials: Y
authors.lastname: Shen
authors.forename: M
authors.initials: M
authors.lastname: Haapasalo
mesh_terms: D000328:Adult; D000818:Animals; D001431:Bacteriological Techniques; D018441:Biofilms / Q000187:drug effects*; D002417:Cattle; D002710:Chlorhexidine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000627:therapeutic use; D024042:Collagen Type I / Q000737:chemistry; D019551:Dental Disinfectants / Q000008:administration & dosage / Q000627:therapeutic use*; D003773:Dental Plaque / Q000382:microbiology*; D017886:Durapatite / Q000737:chemistry; D004492:Edetic Acid / Q000008:administration & dosage / Q000627:therapeutic use; D013293:Enterococcus faecalis / Q000187:drug effects*; D006801:Humans; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000627:therapeutic use; D054023:Lasers, Semiconductor / Q000627:therapeutic use; D008751:Methylene Blue / Q000627:therapeutic use; D050296:Microbial Viability / Q000187:drug effects; D016877:Oxidants / Q000008:administration & dosage / Q000627:therapeutic use; D010778:Photochemotherapy / Q000379:methods; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D012973:Sodium Hypochlorite / Q000008:administration & dosage / Q000627:therapeutic use; D013997:Time Factors
chemical_list: D024042:Collagen Type I; D019551:Dental Disinfectants; D016877:Oxidants; D017319:Photosensitizing Agents; D017886:Durapatite; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D012973:Sodium Hypochlorite; C010882:chlorhexidine gluconate; D002710:Chlorhexidine; D008751:Methylene Blue