Photodynamic suppression of Enterococcus faecalis using the photosensitizer mTHPC

Background and Objectives Enterococcus faecalis is frequently found in persistent endodontic infections. In this context, the antimicrobial photodynamic therapy (aPDT) could become a modern alternative to existing antibacterial treatment approaches. The aim of this study was to investigate the effect of aPDT on E. faecalis using the photosensitizer (PS) 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC) enriched in liposomes. Materials and Methods Enterococcus faecalis was cultivated in Schaedler submerged culture for 24 hours, then isolated and adjusted in PBS to 108 cells/ml. The bacterial suspension was pipetted into a black microtitration plate and incubated for 15 minutes in the dark with mTHPC in various concentrations (10, 30, and 50 µM). The photosensitized suspensions were subjected to laser light (652 nm) at a light fluence of 100 J cm−2 (test group A). In addition, the suspension sensitized with 50 µM mTHPC was irradiated with 25, 50, and 75 J cm−2 (test group B). The following controls were used: non-irradiated bacterial suspension in the absence of mTHPC (C); irradiated bacterial suspension in the absence of mTHPC (D); non-irradiated bacterial suspension incubated with mTHPC (E). Dilution series (100–10−6) were made of all groups and applied on Schaedler agar. After anerobic cultivation (4 days), the colony-forming units (CFU/ml) were determined. Results Enterococcus faecalis was suppressed completely after incubation with 50 µM mTHPC and illumination with 100 J cm−2. Photodynamic treatment with 10 and 30 µM mTHPC caused reduction in CFU by 5.8 and 6.7 log-units. The application of an energy fluence <100 J cm−2 resulted in a decline of antibacterial efficiency. Irradiation of the non-photosensitized solution showed no suppressing impact. Incubation of the PS without additional irradiation caused a maximal reduction in CFU by 1.5 log-units. Conclusion The results show that aPDT using the PS mTHPC incorporated in liposomes could be a new approach to adjuvant treatment of endodontic infections with E. faecalis. Lasers Surg. Med. 43:241–248, 2011. © 2011 Wiley-Liss, Inc.