Antimicrobial photodynamic therapy by continuous and switched mode irradiation against Enterococcus faecalis and Cutibacterium acnes

Abstract

Photodynamic therapy (PDT) has been used against bacterial, fungal and viral infections and recently demonstrated that there is no development of resistance by microorganisms. PDT consists of the activation of a photosensitizer (non-toxic dye) by light in an adequate wavelength, where the generation of reactive oxygen species (type I reaction) or energy transfer to the oxygen will lead to the production of oxygen singlet (type II reaction) causing cell death. Some of the photosensitizers used in the therapy are chlorins (reduced porphyrins), curcumin (natural dye extracted from Curcuma longa L. rhizomes) and methylene blue (cationic dye). PDT has been used as an adjuvant treatment in periodontics, implantology and endodontics to reduce the remaining microorganisms after mechanical treatment. The genus Enterococcus is part of the group of gram-positive, facultative anaerobic bacteria, residents of the gastrointestinal tract, vaginal and oral cavity. It is associated with endodontic infections and is resistant to intracanal drugs. In addition, TFD has been studied to be applied when root canal treatment fails where E. faecalis is able to survive as a single organism or as an important component of this flora. In addition to the genus Enterococcus, the genus Propionibacterium is also found in primary and persistent endodontic infections, and the species Cutibacterium acnes, formerly known as Propionibacterium acnes, is the most frequent species. Cutibacterium acnes (C. acnes) is a facultative anaerobic gram-positive bacterium that normally colonizes human sebaceous glands. Our rechearch group has observed that these two strains presented different responses in relation to light doses and the mode of irradiation also seems to be important. In this way, the present study aims to evaluate the phototoxicity of the irradiation in switched and continuous mode in PDT in strains of Enterococcus faecalis and Cutibacterium acnes, in suspension and in biofilm phase, using as photosensitizers methylene blue, chlorine and curcumin. (AU)