Organic light emitting diode for in vitro antimicrobial photodynamic therapy of Candida strains

•OLED devices are effective light sources for aPDT.•The present work expands the range of microbes that can be treated by OLED devices.•Fractionating a given light dose gave more effective inhibition for aPDT. Organic light emitting diodes (OLEDs) are very attractive light sources because they are large area emitters, and can in principle be deposited on flexible substrates. These features make them suitable for ambulatory photodynamic therapy (PDT). A few reports of in vitro or in vivo OLED based PDT studies for cancer or microbial inhibition are published but to our best knowledge, none against yeasts. Yeast infections are a significant health risk, especially in low income countries with limited medical facilities. In this work, OLED-based antimicrobial PDT (aPDT), using methylene blue (MB) as photosensitizer (PS), is studied to inactivate opportunistic yeast of four Candida strains of two species: Candida albicans and Candida tropicalis. Before aPDT experiments, fluconazole-resistance was evaluated for all strains, showing that both strains of C. tropicalis were resistant and both strains of C. albicans were sensitive to it. We found that 3 repetitive irradiations work better than a single dose while keeping the total fluence constant, and that this result applies whether or not the strains are resistant to fluconazole.