Ação fototóxica do laser em baixa intensidade e diodo de emissão de luz (LED) na viabilidade do fungo Trichophyton rubrum: estudo "in vitro

Abstract

Trichophyton rubrum is the most common micro-organism infecting fungal dermatological lesions. The aim of the present work is to study the effect of low intensity light source (in the red band of the electromagnetic spectrum) on Trichophyton rubrum sample associated to a photosensitizer (Toluidine Blue). Two light sources were employed in the tests: diode laser (660 nm, power output of 100 mW, exposition time of3 minutes) and LED (630 nm, power output of 100 mW, exposition time of 3 minutes). Toluidine Blue (TBO) was chosen due to its optical (maximal absorption in the wavelengths of the laser and the LED sources) and biochemical (well absorbed by fungi cells) properties. Trichophyton rubrum were suspended in a standard solution and six test groups were prepared with a final suspension volume of 1000 L. Group 1: growthcontrol without treatment; Group 2: inoculum suspension exposed to LED irradiation; Group 3: inoculum suspension exposed to laser irradiation; Group 4: 100 L of TBO added to 900 L of inoculum; Group 5: 100 L of TBO added to 900 L of inoculum and exposed to LED irradiation; Group 6: 100 L of TBO added to 900 L of inoculum and exposed to laser irradiation. The irradiation time was 3 minutes for Groups 2, 3, 4, 5 and 6. For Groups 5 and 6 it was observed 5 minutes of pre-irradiation time (PIT) after the introduction of TBO and before irradiation. The results exhibited significant differences between Groups 5 and 6 with 68.1% and 56% reduction, respectively, regarding the number of viable colonies. LED source generates a non-coherent light beam, presenting bigger divergence if compared to the laser beam. As consequence, it encompassed a bigger volume of inoculum suspension, bringing, by this way, its phototoxic action to a bigger number of cells.