Visualizing Biomaterial Degradation by Candida albicans Using Embedded Luminescent Molecules To Report on Substrate Digestion and Cellular Uptake of Hydrolysate

Microbial pathogens use hydrolases as a virulence strategy to spread disease through tissues and colonize medical device surfaces; however, visualizing this process is a technically challenging problem. To better understand the role of secreted fungal hydrolases and their role in Candida albicans virulence, we developed an in situ model system using luminescent Re­(I) and Ir­(III) containing probe molecules embedded in a biodegradable (poly­(lactic-co-glycolic acid), PLGA) polymer and tracked their uptake using epifluorescent imaging. We found that secretion of esterases can explain how physically embedded probes are acquired by fungal cells through the degradation of PLGA since embedded probes could not be liberated from nonbiodegradable polystyrene (PS). It was important to verify that epifluorescent imaging captured the fate of probe molecules rather than naturally occurring fungal autofluorescence. For this, we exploited the intense luminescent signals and long spectral relaxation times of the Re and Ir containing probe molecules, resolved in time using a gated imaging system. Results provide a visual demonstration of a key virulence trait of C. albicans: the use of hydrolases as a means to degrade materials and acquire hydrolysis products during fungal growth and hyphal development. These results help to explain the role of nonspecific hydrolases using a degradable material that is relevant to the study of fungal pathogenesis on biotic (tissues) surfaces. Additionally, understanding how fungal pathogens condition surfaces by using nonspecific hydrolases is important to the study of fungal attachment on abiotic surfaces, the first step in biofilm formation on medical devices.