Photodynamic antimicrobial chemotherapy (PACT) using phenothiazines derivatives associated with the red-orange LED against staphylococcus aureus

The objective of this study was to contribute to PDT development by researching alternative light sources using redorange LED light at doses of 2.4 e 4.8 J/cm2 to evaluate the bactericidal effect of photodynamic antimicrobial chemotherapy (PACT) using phenothiazinium dye (Toluidine blue O and methylene blue) at a low concentration of 1μg/mL on strain of Staphylococcus aureus (ATCC 23529) in vitro. For this research, tests were performed in triplicate and the samples were distributed into six test groups: (L-P-) Negative control (L1+ P-) and (L2+ P-) bacterial suspensions were irradiated with laser energy 2.4 and 4.8 J/cm respectively in the absence of photosensitizer; (L1 + P+) and (L2 + P+) bacterial suspensions were irradiated with laser in the presence of 1μg/ml of photosensitizer and finally (L-P+) bacterial suspensions only in the presence of phenothiazinium dye. Therefore, were analyzed the potential bactericidal PACT by counting of colony-forming units and analyzed statistically (ANOVA, Tukey test, p<0.05). The results demonstrated that comparing the LED group (L2 + P-) with negative control group, LED group (L1+ P-) and photosensitizer group there was a statistically significant (p<0.0001, p<0.01 and p<0.001, respectively) that the group treated only with LED (energy density of 4.8J/cm) increased the average of CFU counts. The negative control group when compared to the groups submitted to PDT only showed a statistically significant reduction (p<0.01) relative to the group (L2+P+) that showed a decrease in the number of CFU. There was no statistically significant difference between the groups submitted to PDT (L1+P+ and L2+P+). Although the results of this study have shown a reduction in average number of colony forming units by the appropriate LED-dye treatment combination, it needs further investigation.