Photodynamic therapy as an alternative treatment for disinfection of bacteria in oral biofilms

Background and Objectives Biofilm-related diseases such as caries and periodontal disease are prevalent chronic oral infections which pose significant oral and general health risks. Biofilms are sessile communities attached to surfaces. Photodynamic therapy (PDT) has been demonstrated to have a significant anti-microbial effect and presents as an alternative to treating biofilm-related disease. The aim of this study was to determine the ability of porfimer sodium induced PDT to treat localized infections of Streptococcus mutans in biofilm communities. Materials and Methods Reproducible biofilms were formed by S. mutans strain ATCC 27351 growing in log phase at 37°C in Brain Heart Infusion medium, circulating through flow cells at 3ml/minute for 36-48hours. The photosensitizer used was porfimer sodium (Photofrin®) at 125μg/ml with biofilm immersion times of 5minutes and increasing energy density of post-immersion laser illumination at 630nm (100mW/cm²). Resulting effects on bacterial viability in the biofilms were tracked by monitoring alamarBlue® conversion. Supplementary data characterizing the biofilms before and after exposure to PDT were acquired by Multiple Attenuated Internal Reflection Infrared Spectroscopy (MAIR-IR). Results The results of this study show that PDT using porfimer sodium and 630nm laser light was effective in significantly reducing the viability of S. mutans biofilms. Maximum effectiveness was seen when biofilms were exposed to both photosensitizer and light versus controls. Porfimer sodium incubation times as short as 5minutes in solutions as dilute as 25μg/ml and illuminated with as little as 30J/cm ² resulted in significant decreases in viability of bacteria in biofilms. Optimum parameters appear to be 125μg/ml porfimer sodium concentration and incubated for 5minutes and 60J/cm² of light energy density. Conclusions This study has demonstrated that significant killing of the cariogenic organism S. mutans by the combination of a photosensitizer and the appropriate wavelength of laser light was possible even when the bacteria are embedded in an extracellular matrix. Lasers Surg. Med. 44: 588-596, 2012. © Wiley Periodicals, Inc.