Photodynamic action of the red laser on Propionibacterium acnes*

BACKGROUND Photodynamic therapy is a therapeutic modality that has consolidated its activity in the photooxidation of organic matter, which arises from the activity of reactive oxygen species. OBJECTIVE To evaluate the effect of red laser 660nm with the photosensitizer methylene blue on Propionibacterium acnes in vitro. METHOD The experimental design was distributed into four groups (1 - control group without the application of light and without photosensitizer, 2 - application of light, 3 - methylene blue without light, and 4 - methylene blue with light). Tests were subjected to red laser irradiation 660nm by four cycles of 5 minutes at 3-minute intervals. RESULTS It was evidenced the prominence of the fourth cycle (20 minutes) groups 2, 3 and 4. STUDY LIMITATIONS Despite the favorable results, the laser irradiation time photosensitizer associated with methylene blue were not sufficient to to completely inhibit the proliferation of bacteria. CONCLUSION Further studies in vitro are recommended to enable the clinical application of this photosensitizer in photodynamic therapy.