3–7.4 for ROS-quencher studies. Cell viability was assessed by counting the number of colony-forming units (CFUs)

after an incubation period of 48 h Metabolism inhibitor at 35 °C on SB. The sample attenuance was adjusted to either 0.5 (for 3 log10 CFU ml−1 reduction and ROS-quencher’s studies) or 4 (for 6 log10 CFU ml−1 reduction assays) McFarland values. Starting from 24-h-old yeast cultures, suspensions of the desired McFarland value (0.5 for 3-log10 CFU-reduction studies and 4 for 6-log10 CFU-reduction studies) were prepared in bi-distiled water. Ninety microlitres of these initial suspensions was dropped in different wells of a microtitre plate and different concentrations of HYP or DMMB, both of them in the range 0.32–40 μmol l−1, were added. The plates were then maintained at 35 °C in the dark for different periods of time (0, 15, 30, 60 min, 3, 5 and 24 h) to evaluate the influence of contact time on the outcome of the photodynamic treatments. Afterwards, yeast cells were subjected to LED illumination with a fluence of either 18 or 37 J cm−2. Fungal cultures grown under the same conditions with and without PS, either kept in the dark or illuminated, served as controls. After

the treatments, samples and controls were incubated at 35 °C for 48 h, and the antifungal effect was determined by counting the number of CFU per millilitre in samples and controls. We adopted the criterion used to define bactericidal activity as the definition for fungicidal activity namely a 99.9%, or 3 log10, reduction in CFU per millilitre selleck screening library from the starting inoculum. This criterion has been used previously to assess the antifungal activity of drugs Histone demethylase against Candida spp.[17] A more stringent criterion of 99.9999% or 6 log10 unit decrease

was also adopted for the purpose of assessing how far we could go without inducing significant phototoxicity to skin cells.[9] An aliquot of 90 μl of 0.5 McFarland yeast suspensions in PBS buffer at pH 7.3–7.4 was merged with PBS solutions containing the desired ROS-quencher. Thus, SA 80 mmol l−1 (quencher of 1O2), MAN 100 mmol l−1 (using 1% DMSO) (quencher of *OH), CAT 1880 U ml−1 (CAT, quencher of H2O2) or, SOD 200 U ml−1 (SOD, quencher of O■−2) were added separately to the cells and kept in the dark for 15 min at 35 °C.[18, 19] Afterwards the HYP or DMMB concentration required for 3-log10 CFU reduction was added and incubated for 1 min (HYP) or 15 min (DMMB). The suspensions were then irradiated using 18 J cm−2 of fluence. Fungal cultures grown under the same conditions without quenchers served as controls. After the treatments, samples and controls were incubated at 35 °C for 48 h, and the antifungal effect was determined by counting the number of CFUs. Data are presented as mean and standard deviation. All the experiments were performed in triplicate and repeated at least three times.