Cryptococcosis is an infection caused by the encapsulated yeast Cryptococcus neoformans and the most afflicted sites
are lung, skin and central nervous system. A range of studies had reported that photodynamic therapy (PDT) can
inactivate yeast cells; however, the in vivo experimental models of cryptococcosis photoinactivation are not commonly
reported. The aim of this study was to investigate the ability of methylene blue (MB) combined with a low-power red
laser to inactivate Cryptococcus neoformans in in vitro and in vivo experimental models. To perform the in vitro study,
suspension of Cryptococcus neoformans ATCC-90112 (106cfu/mL) was used. The light source was a laser (Photon Lase
III, DMC, São Carlos, Brazil) emitting at λ660nm with output power of 90mW for 6 and 9min of irradiation, resulting
fluences at 108 and 162J/cm². As photosensitizer, 100μM MB was used. For the in vivo study, 10 BALB/c mice had the
left paw inoculated with C. neoformans ATCC-90112 (107cfu). Twenty-four hours after inoculation, PDT was performed
using 150μM MB and 100mW red laser with fluence at 180J/cm2. PDT was efficient in vitro against C. neoformans in
both parameters used: 3 log reduction with 108J/cm² and 6 log reduction with 162J/cm². In the in vivo experiment, PDT
was also effective; however, its effect was less expressive than in the in vitro study (about 1 log reduction). In
conclusion, PDT seems to be a helpful alternative to treat dermal cryptococcosis; however, more effective parameters
must be found in in vivo studies.
It has been proposed that photodynamic therapy (PDT) can inactivate microbial cells. A range of photosensitizers and light sources were reported as well as different fluence parameters and dye concentrations. However, much more knowledge regarding to the role of fluences, irradiation time and irradiance are required for a better understanding of the photodynamic efficiency. The aims of this study were to investigate the role of light parameters on the photoinactivation of yeast cells, and compare cell survivors in different growing phases following PDT. To perform this study, a
suspension (10<sup>6</sup>cfu/mL) of <i>Candida albicans</i> ATCC-90028 was used in log and stationary-phase. Three irradiances 100mW/cm<sup>2</sup>, 200mW/cm<sup>2</sup> and 300mW/cm<sup>2</sup> were compared under 3min, 6min and 9min of irradiation, resulting in fluences of 18, 36, 54, 72,108 and 162J/cm<sup>2</sup>. The light source used was a laser emitting at 660nm with output power of 30, 60 and 90mW. As photosensitizer, 100μΜ methylene blue was used. PDT was efficient against yeast cells (6 log reduction) in log and stationary-phase. Neither photosensitizer nor light alone presented any reduction of cell viability. The increase of irradiance and time of irradiation showed a clearly improvement of cell photoinactivation. Interestingly, the same fluences in different irradiances presented dissimilar effects on cell viability. The irradiance and time of irradiation are important in PDT efficiency. Fluence per se is not the best parameter to compare photoinativation effects on yeast cells. The growing-phases presented the same susceptibility under <i>C. albicans</i> photoinactivation.