title: Influence of bacterial growth modes on the susceptibility to light-activated disinfection.
abstract: OBJECTIVE
  To evaluate the efficacy of light-activated disinfection (LAD) using methylene blue (MB) and a non-coherent light source on gram-positive and gram-negative bacteria in different growth modes. The influence of different photosensitizer (PS) formulations in the MB-mediated LAD of biofilms was also evaluated.
  
  
  METHODS
  Light-activated disinfection using MB was tested on Enterococcus faecalis in a planktonic suspension, coaggregated suspension and mono-species biofilms and on Pseudomonas aeruginosa in a planktonic suspension and mono-species biofilms. Further, the difference in susceptibility of E. faecalis and P. aeruginosa biofilms to LAD with modified PS formulations was assessed by conventional culturing methods and confocal laser scanning microscopy (CLSM).
  
  
  RESULTS
  Higher energy dose was required for LAD of bacteria in a coaggregated suspension and in biofilm compared to their planktonic counterparts. Biofilm mode of growth offered the greatest resistance to LAD in both the tested strains of pathogens (P<0.001). Gram-positive E. faecalis was more susceptible to LAD than the gram-negative P. aeruginosa, and the use of modified PS formulations was found to enhance the efficacy of LAD to destroy the biofilm (P<0.001).
  
  
  CONCLUSIONS
  Bacterial growth modes play a vital role in influencing the susceptibility to LAD in a dose-dependent manner. The nature of the PS formulation influences the susceptibility of biofilms to LAD.
authors: Faculty of Dentistry, Department of Restorative Dentistry, National University of Singapore, Singapore.
authors: M H
authors: MH
authors: Upadya
authors: A
authors: A
authors: Kishen
mesh_terms: D058491:Bacterial Load; D001431:Bacteriological Techniques; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D002626:Chemistry, Pharmaceutical; D004203:Disinfection / Q000379:methods*; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D013293:Enterococcus faecalis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008751:Methylene Blue / Q000008:administration & dosage / Q000737:chemistry / Q000627:therapeutic use; D018613:Microscopy, Confocal; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000008:administration & dosage / Q000737:chemistry / Q000627:therapeutic use*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000502:physiology*; D011829:Radiation Dosage; D018915:Root Canal Preparation / Q000379:methods
chemical_list: D017319:Photosensitizing Agents; D008751:Methylene Blue