Chlorophyllin-based Photodynamic Inactivation against Candidozyma auris planktonic cells and dynamic biofilm

Candidozyma auris likely gained thermotolerance as a result of climate change and emerged from its origin in Indian wetlands to a severe healthcare threat because of its resistance to common antifungals and antiseptics in only a few decades. This development identifies the yeast as a perfect example for the relevance of the One Health concept for human well-being. Here, we compare the effectiveness of Photodynamic Inactivation (PDI) based on the economic and ecofriendly natural photosensitizer sodium-magnesium-chlorophyllin (Chl) to that of a synthetic chlorin e6 derivative carrying cationic moieties, B17-0024, suggesting both as alternative to common disinfectants against C. auris. Experiments were conducted on planktonic cells and-for the very first time-on dynamic biofilms using the CDC bioreactor. Treatment of planktonic cells with 50 µM Chl and blue light (395 nm, 7.5 J cm^-2, 15 min drug to light interval) achieved a 7 log₁₀ step reduction of viable C. auris. B17-0024 induced a more than 5 log₁₀ step photokilling at 10 µM. Illumination of the same concentrations with red light (600-700 nm, 30 J cm^-2) resulted in a relative inactivation of 7 log₁₀ steps for Chl and 6 log₁₀ steps for B17-0024. Dynamic biofilm samples were illuminated with 3.33-times higher radiant exposure (25 J cm^-2 at 395 nm or 100 J cm^-2 at 600-700 nm). The antimicrobial effect of a 99.9% reduction of C. auris was exceeded with 10 µM B17-0024 and blue light illumination and with 50 µM Chl and B17-0024 activated by red light. Biofilms were completely eradicated when doubling the photosensitizer concentrations. Our results demonstrate that PDI based on Chl represents a rapid and effective tool to eliminate emerging pathogens even if resistant to conventional treatment. Due to its low costs and eco-friendliness PDI based on Chl may be applicable for disinfection of larger areas in hospitals.