Photodynamic Therapy in Candida spp. and Epithelial Cell Cultures: An In vitro Study

Aims: The objective of this study was to determinate the photodynamic effect using methylene blue and diode laser on Candida spp. and epithelial cells in vitro.

Study Design: An in vitro study was carried on using cultures of Candida spp. and HEp-2 cells.

Place and Duration of Study: This study was developed at the School of Biosciences of the Department of Microbiologic Sciences and at the Laboratory of Pneumology of the Biomedical Research Institute at São Lucas Hospital, both at the Pontifical Catholic University of Rio Grande do Sul, located in Porto Alegre, Brazil, between January and December.

Methodology: Cultures of Candida spp. and HEp-2 cells were submitted to aPDT with methylene blue (100 μg/mL) and indium-gallium-aluminum-phosphide (InGaAlP) diode laser at 100 J/cm2, 270 J/cm2 and 450 J/cm2.

Results: All of these three doses caused significant inactivation of Candida spp. (P<0.05). At 450 J/cm2, the viability of Candida spp., based on colony forming units (CFUs), was reduced by 72.42%, followed by lesser effects with 270 J/cm2 and 100 J/cm2, 45.87% and 22.83%, respectively. PDT decreased CFUs by 50.44% in C. albicans, while other Candida species showed a 41.18% decline in CFUs (P<0.05). With regard to the average effect of the three doses tested in PDT group, HEp-2 cell viability, based on trypan blue exclusion, declined to 70.81%, which was significantly lower than that observed in the control group (86.21%).

Conclusion: Methylene blue plus laser exposure (100 J/cm2, 270 J/cm2 and 450 J/cm2) caused significant inactivation of Candida spp. Photodynamic inactivation of the epithelial cells based on cell viability was 2.24-fold lower than the inactivation of Candida spp., which suggests a safety margin for in vivo application.