Optical tweezers reveal increased intracellular viscosity in Candida tropicalis after APDT

Fungal infections in humans have significantly increased, primarily due to various Candida species such as Candida albicans, Candida tropicalis, and Candida auris, along with a rise in antifungal resistance. In response to these challenges, new strategies like antimicrobial photodynamic therapy (APDT) have been explored. However, understanding the specific cellular responses to these treatments remains a challenge. In this context, microscopic manipulation with optical tweezers (OT) emerges as a valuable tool for investigating these responses. <br/> <br/> A novel method combining OT and APDT is presented to monitor the effects of treatments on individual fungal cells, focusing on C. tropicalis. Cells were placed in a 96-well microplate with Sabouraud dextrose broth to create biofilms and promote the formation of opaque cells by phenotypic switching. Methylene blue with a 10 &mu;M concentration was added to the cells and irradiated with a lethal light dose of 60 J cm^-². Subsequently, an intracellular lipid body was captured using an OT system and the stiffness of the trap over time was determined by analyzing its Brownian motion. The results revealed an increase in the intracellular viscosity during cell death processes activated by the application of APDT. This multifaceted methodology lays the foundation for formulating more effective therapeutic strategies against fungal infections.