The antimicrobial activity of photodynamic therapy against Streptococcus mutans using different photosensitizers
Several photosensitizers have been used against oral bacteria without standardization. Singlet oxygen (1O2) is an aggressive chemical species that can kill cells through apoptosis or necrosis. Objective: to compare the antimicrobial activity of photodynamic therapy (PDT) with different photosensitizers at the same concentration against Streptococcus mutans. In addition, the 1O2 production of each photosensitizer was determined. The photosensitizers (163.5 μM) methylene blue (MB), toluidine blue ortho (TBO) and malachite green (MG) were activated with a light-emitting diode (LED; λ = 636 nm), while eosin (EOS), erythrosine (ERI) and rose bengal (RB) were irradiated with a curing light (λ = 570 nm). Light sources were operated at 24 J cm−2. For each photosensitizer, 40 randomized assays (n = 10 per condition) were performed under one of the following experimental conditions: no light irradiation or photosensitizer, irradiation only, photosensitizer only or irradiation in the presence of a photosensitizer. After treatment, serial dilutions of S. mutans were seeded onto brain heart infusion agar to determine viability in colony-forming units per milliliter (CFU mL−1). Generation of 1O2 was analyzed by tryptophan photooxidation, and the decay constant was estimated. Results were analyzed by one-way ANOVA and the Tukey–Kramer test (p < 0.05). PDT with irradiation in the presence of the photosensitizers TBO and MG was effective in reducing S. mutans counts by 3 and 1.4 logs, respectively (p < 0.01), compared to their respective untreated controls. MB generated 1.3 times more 1O2 than TBO, and both produced significantly higher concentrations of singlet oxygen than the other photosensitizers. Since in vitro bulk 1O2 production does not indicate that 1O2 was generated in the bacterial activity site, the bactericidal action against S. mutans cannot be related to in vitro singlet O2 generation rate. In vitroS. mutans-experiments demonstrated TBO as the only photosensitizer that effectively reduced 99.9% of these microorganisms.
► Red and blue light sources activated sensitizers with corresponding wavelength. ► Photodynamic therapy with toluidine blue reduced S. mutans with biological relevance. ► Methylene blue generated the greatest reduction in the concentration of tryptophan. ► Photosensitizers with distinct characteristics result in variable activity in cells.
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 106, 5 January 2012, Pages 40–46