Efficient in vitro photodynamic inactivation using repetitive light energy density on Candida albicans and Trichophyton mentagrophytes.

Background: We compared the effectiveness of a single irradiation vs repetitive irradiation of light, for in vitro photodynamic inactivation (PDI) of Candida albicans and Trichophyton mentagrophytes, by using methylene blue (MB) and rose bengal (RB) as photosensitizers (PS).

Methods: MB from 5 to 60 μM and RB from 0.5 to 10 μM, with energy densities from 10 to 60 J/cm, were tested in C. albicans. We further optimize the PDI by reducing the light energy density and PS concentration for the single irradiation experiments by using repetitive doses (two and three times). MB was tested in C. albicans and T. mentagrophytes, and RB was tested in C. albicans.

Results: MB-PDI and RB-PDI in C. albicans significantly reduced the number of colony-forming units per milliliter (CFU/mL) when compared to the control groups. Using a single irradiation, over 99% growth inhibition of C. albicans was obtained with MB at 20 μM-60 J/cm, and with RB at 1 μM-30 J/cm and 5 μM-10 J/cm. With repetitive doses, similar results were obtained by reducing several times the light energy density and the PS concentration for C. albicans and T. mentagrophytes.

Conclusions: The results showed that RB was more effective than MB for C. albicans inactivation. In addition, it is possible to significantly reduce the amount of PS and light energy density requirements by using repetitive irradiations in both genera tested. It makes the technique less invasive and could reduce the side effects in people extremely sensitive to the PS or the light.