The role of Candida auris extracellular vesicles on pathogenesis and treatment

Abstract

Candida auris is an emergent pathogenic fungus prominently known for its unusual transmissibility, environmental persistence, and multidrug resistance. It is the only fungi to be listed in the highest priority for the American Centers for Disease Control’s Antimicrobial Resistance Threats List. Until now, few of its known antifungal resistance mechanisms could adequately explain differences in survival in vitro and in vivo when challenged with antifungal drugs. Therefore, research into phenotypic survival mechanisms for C. auris was undertaken.

Here, naturally produced nanometer-sized secreted particles known as extracellular vesicles (EVs) are shown to play a key role in attenuating the potency of the essential frontline drug, amphotericin B. In in vitro assays, these EVs acted in a dose-dependent manner, with nanogram levels of them capable of doubling the minimum inhibitory concentration needed to kill the yeast. The results were reproducible in drastically different clinical formulations of the drug as well, suggesting a possible clinical translation to the research. Furthermore, this effect proved reproducible and transferable among isolates of C. auris, though could not be replicated in other pathogenic fungi such as Candida albicans. Chemical ablation of EV endocytosis restored wild-type susceptibility towards the drug in the face of EV treatment. Proteomic analysis of C. auris EVs revealed the abundance of an uncharacterized protein suspected to have glucanase activity. Its nearest homologue in C. albicans revealed potential functions in both dampening immune responses and biofilm catalysing ability. Quantification of C. auris EVs incubated with amphotericin B suggested that EVs likely were not inducing resistance through reducing drug bioavailability.

Together, these results reveal extracellular vesicles to likely be a novel and unique mechanism for the pathogenic yeast C. auris to evade amphotericin B treatment. Successful inhibition of this process restored wild-type susceptibility and provide justification for research into synergies between EV-inhibiting and existing antifungal drugs. Further research will be required to detail the exact mechanism in which C. auris EVs confer resistance against amphotericin B, and whether these results can be clinically translated.