Effect of different wavelengths and dyes on Candida albicans: In vivo study using Galleria mellonella as an experimental model

Background Studies on photodynamic inactivation against microorganisms had a great development in recent years. The aim of this work was to test the application of different laser wavelengths with or without different photosensitizing dyes on Candida albicans cells in vitro and in photodynamic therapy protocols in vivo in larvae of Galleria mellonella. Methods Laser application was realized on C. albicans cells suspended in saline solution or cultured on solid medium for the in vitro study, and in a model of G. mellonella candidal infection for the in vivo study. Three wavelengths (650, 405, and 532 nm) were used in continuous mode with different values of applied fluences: 10, 20 and 30 J/cm2 for the in vitro study and 10 J/cm2 for the in vivo study, without and with photosensitizing dyes. Results No growth inhibition was obtained on yeast cells in saline solution without photosensitizers. The maximum inhibition of growth (100%) was obtained with 405 nm diode laser and curcumin at any used fluence. No growth inhibition was observed for yeast cells cultured on solid medium after laser application without dyes. An inhibition was observed after laser application when curcumin and erythrosine were added to the medium. The survival curves of G. mellonella larvae infected with C. albicans with or without the different dyes and after laser application showed a statistically significant difference (p < 0.001) in comparison with the proper control groups. Conclusions These results show the efficacy of photodynamic inactivation exploiting a suitable combination of light and dyes against C. albicans and the potential of photodynamic therapy for the treatment of candidal infections