Photodynamic therapy mediated by chlorin-type photosensitizers against Streptococcus mutans biofilms

Photodynamic therapy (PDT) can be used for the control of oral pathogens and different photosensitizers (PS) have been investigated. This study evaluated the efficacy of PDT against Streptococcus mutans biofilms using two second-generation PS derived from chlorin: Photoditazine® (PDZ) and Fotoenticine® (FTC). These PS were compared to methylene blue (MB), a dye with proven antimicrobial activity against S. mutans. Suspensions of S. mutans were cultured in contact with bovine tooth disks for biofilm formation. After 48 h, the biofilms were treated with PDZ (0.6 mg/mL), FTC (0.6 mg/mL) or MB (1 mg/mL) and submitted to laser irradiation (660 nm, 50 mW/cm²). The biofilms were quantified by the determination of CFU/mL count and analyzed by scanning electron microscopy (SEM). All PS used for PDT reduced the number of S. mutans, with a statistically significant difference compared to the untreated groups. PDT achieved microbial reductions of 4 log with MB and 6 log with PDZ, while the use of FTC resulted in the complete elimination of S. mutans biofilms. SEM analysis confirmed the CFU/mL results, showing that all PS, particularly FTC, were able to detach the biofilms and to eliminate the bacteria. In conclusion, PDT mediated by chlorin-type PS exhibited greater antimicrobial activity against S. mutans than MB-mediated PDT, indicating that these PS can be useful for the control of dental caries.