Atividade antimicrobiana da terapia fotodinâmica sobre streptococcus mutans in vitro

Abstract

Photodynamic therapy (PDT) is based on the use of a light source in combination with photosensitizing agents, which initiate a photochemical reaction that leads to cell destruction. Since the literature has demonstrated the potential of PDT to promote bacterial killing, the purpose of this study was to evaluate the influence of the preirradiation and exposure time in the antimicrobial effect of photodynamic therapy (PDT) on suspensions of S. mutans in vitro (ATCC 25175). MATERIALS AND METHODS: Nine groups was evalueted, with three samples each (n = 3). Group 1 contained 1 ml of standardized suspension (inoculum) and received no treatment, being used as a control. In groups 2 and 3 the activity of the dye and the light source were tested separately. The toxicity of methylene blue was assessed with the G2 leaving 0.75ml inoculum and 0.25 methylene blue without action of the halogen light. To evaluate the toxicity of light alone without dye, 1 ml of standardized suspension was irradiated by halogen light for 1 min (G3). In the other six groups, the bacterial suspensions were subjected to photodynamic therapy, in association with methylene blue to 25 mg / L to a halogen light source. The preirradiation time is the period in which the dye is left in contact with the substrate prior to application of light. For groups 4, 5 and 6 preirradiation time was five minutes and the exposure time ranged from 1 min for G4, G5 and 30s to the 20s for the G6. The same exposure times were used respectively for the groups 7, 8 and 9, but with a preirradiation time of three minutes. Serial dilutions were performed up to 103 CFU, and 20l aliquots were plated in triplicate on mitis salivarius agar. The count of CFU was obtained visually after incubation in a microaerophilic atmosphere at 37 ° C for 48 hours. RESULTS: The results showed that groups 2 and 3 showed no significant bacterial reduction in the control group. In groups where PDT was performed, reducing the time preirradiation and exposure caused a reduction in the antimicrobial effect. Groups 4 and 5 showed statistically significant results, when using an exposure time of 60s and 40s and preirradiation time of 5 min. The other groups 6, 7, 8 and 9, showed no statistically significant differences in relation to the antimicrobial effect of PDT. For these groups, reducing the exposure time did not affect the results significantly. CONCLUSION: PDT under the conditions used in the experiment presented antimicrobial potential, which was affected by the time variation of the preirradiation and exposure time.