C. elegans as a tractable infection model for the emerging fungal pathogen Candida auris

Candida auris is an emerging multidrug-resistant fungal pathogen. The genetic factors contributing to the virulence, drug resistance, and stress-tolerant nature of C. auris are mostly unknown. Additional animal models of virulence are needed, especially those amenable to high-throughput analysis. The nematode Caenorhabditis elegans has been validated as an effective tool for studying multiple fungal and bacterial pathogens. We describe here a C. elegans infection model in which exposure to C. auris is lethal to worms with kinetics similar to killing by Candida albicans; in contrast to C. albicans, C. auris does not form hyphae, indicating distinct virulence mechanisms. Furthermore, an engineered mutant auxotrophic for adenine biosynthesis (ade2∆) is avirulent, as it is in many models, indicating that the nematode can discriminate between virulent and avirulent mutants. Moreover, the C. elegans model can recapitulate strain-to-strain differences in virulence seen in mouse models. We have adapted a live/dead staining methodology using SYTOX Orange to enable a high-throughput assay amenable to analysis of multiple strains or genetic mutants. This model has significant advantages, including cost-effectiveness, a short generation time, and excellent amenability to high-throughput assays. C. elegans represents a valuable preliminary screening platform for C. auris virulence studies.

Candida auris is a growing clinical problem. This fungal pathogen spread rapidly worldwide after its discovery in 2009. It avidly colonizes the skin and abiotic surfaces, and many strains are multidrug resistant, making them easy to spread in hospital settings and very difficult to treat. Though distantly related to Candida albicans, it is clear that C. auris possesses unique virulence mechanisms, making studies directly in this species imperative. However, existing animal models, including mouse and invertebrate species, have limitations in variability and throughput. We describe here a facile infection model using the nematode Caenorhabditis elegans, which has previously been used for other bacterial and fungal pathogens. We show that this model can identify virulence differences between strains and in mutants predicted to be less virulent. Moreover, this model is amenable to high-throughput screening. This will be a valuable tool in uncovering C. auris-specific virulence traits.