Photodynamic efficacy of toluidine blue O against mono species and dual species bacterial biofilm.

Aim: The purpose of this study was to investigate how Enterococcus faecalis and Streptococcus mutans behave in mono and dual species biofilm after photodynamic treatment.
Background: Antimicrobial photodynamic therapy (aPDT) leads to the generation of reactive oxygen species (ROS) that destroys bacterial cells in presence of a photosensitizer, visible light, and oxygen.
Material and Methods: We have taken Enterococcus faecalis and Streptococcus mutans as monospecies culture and their dualspecies culture biofilm. Antibacterial effect was evaluated by colony forming unit while antibiofilm action by crystal violet and congored binding assays.
Results: We found that dual species biofilm are more resistant than monospecies biofilm and S. mutans shows dominance over E. faecalis in dual species biofilm, it inhibited the growth of E. faecalis in dual species biofilm. Antibiofilm efficacy of TBO also validated that dualspecies show less inhibition than monospecies biofilm this may be due to different EPS constitution in dualspecies biofilm, hence less inhibition was observed in EPS production of dualspecies biofilm than monospecies biofilm. Reactive oxygen species and singlet oxygen yield was found to be light dose dependent and antimicrobial photodynamic efficiency is directly related to the ROS production.
Conclusion: We conclude that dual species biofilm shows resistance over monospecies biofilm and S. mutans in dual species inhibits the growth of E. faecalis.
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