Antimicrobial photodynamic therapy on Candida albicans pre-treated by fluconazole delayed yeast inactivation

Abstract

Antimicrobial photodynamic therapy (APDI) has been used to treat localized infection and the aim of this study was to evaluate the effect of APDI combined with fluconazole in suspension of Candida albicans. C. albicans ATCC90028 was subcultured onto Sabouraud agar and inocula were prepared at yeast density of 1 × 106 CFU/mL. Methylene blue (MB) was used with concentration of 100 mM. Yeast cells were incubated for 30 min in 24-well plate and then irradiated by LED (660 nm; 690 mW; A = 2.7 cm2; I = 250 mW/cm2) with radiant exposure of 30, 60, and 120 J/cm2. The same APDI setup was used with 2 h fluconazole (0.5 μg/mL) incubation. A UV–vis optical absorption spectroscopy was achieved following fractionated irradiation up to 960 s. There were substantial differences in the killing effect following MB-mediated APDI and C. albicans was eradicated in the both APDI groups. The fluconazole combined to APDI delayed the complete inactivation of the yeast (p < 0.05). Spectroscopy showed a decrease in absorption following irradiation for all absorption peaks. APDI presented an antagonist effect in the presence of fluconazole.