Photoacoustic Spectroscopy of Candida albicans Treated with Methylene Blue

Abstract

In the present work the phototoxic effect of methylene blue (MB) on Candida albicans cultures was studied using the photoacoustic spectroscopy (PAS) technique. An aliquot of 50 μL of C. albicans suspension—strain ATCC 10-231—was incubated with 50 μL of MB solution (0.5 mg/mL), at room temperature. After the proper incubation time, a colony forming unit (CFU) with approximately 3 mm diameter was chosen in each plate. The CFU selected was irradiated using an InGaAlP laser during 20 s. After irradiation and new incubation, the CFUs were collected and stored at −70 °C, until spectroscopy analysis. The spectroscopy analysis was performed using an open PAS setup. The study was conducted in different groups: (1) control (non-treated); (2) irradiated with laser light; (3) treated with MB (non-irradiated); and (4) treated with MB and irradiated with laser light. The PAS measurements were performed on C. albicans in a sterile physiological solution. The measurements indicate that the presence of MB and irradiation promotes a change in the redox state of the cells to the reduced state. The absorption spectrum after photodynamic therapy (PDT) was observed 12 h and 36 h later. It was inferred that PDT can be related to structural changes in cytochrome molecules after 36 h. It is concluded that MB can be an efficient photosensitizer in C. albicans through modification of the cytochrome molecule affecting the cell metabolism.