Visible Light Activation for Fungal Biofilm Inhibition: Combining Antimicrobial Photodynamic Therapy with Singlet Oxygen and Iodine Generation against Candida albicans and Pichia kudriavzevii

Biofilms formed by Candida albicans and the highly resistant Pichia kudriavzevii are critical virulence factors because of their resistance to conventional antifungals. This study explored antimicrobial photodynamic therapy (aPDT) using sulfonated polystyrene nanoparticles with an encapsulated tetraphenylporphyrin photosensitizer (TPP-NPs), synergistically enhanced by potassium iodide (KI), to combat biofilms of these yeasts. TPP-NPs irradiated by visible light generate antimicrobial singlet oxygen (O2(1Δg)), which oxidizes KI to form another reactive species (I2/I3–), augmenting total antimicrobial effects. The usage of TPP-NPs led to reduced cell proliferation and biofilm viability in both species, with KI significantly enhancing efficacy and enabling lower TPP-NP doses. P. kudriavzevii biofilms were more susceptible (70–80% inhibition, up to 95% with KI) than C. albicans biofilms (30–40% inhibition), a crucial finding for drug-resistant P. kudriavzevii. This is the first demonstration that aPDT using TPP-NPs effectively reduces both biofilm formation and viability, especially against resistant P. kudriavzevii, highlighting its potential as a biocompatible alternative therapy for biofilm-associated infections.