A Tractable Nematode Model for the Emerging Fungal Pathogen, Candida auris

Melissa Martinez, BS (Advisor: Michael Lorenz, PhD)

           Candida auris is an emerging multidrug-resistant opportunistic fungal pathogen. It poses a significant threat to immunocompromised patients and those with prolonged stays in healthcare facilities. C. auris spreads rapidly in health care facilities through enhanced colonization of skin and abiotic surfaces. The genetic factors contributing to this ability and to the virulence, drug resistance, and stress-tolerant nature of C. auris are largely unknown. Current animal models of C. auris infections are not well standardized and report conflicting results. 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. In this thesis, I describe a C. elegans infection model in which C. auris is lethal to worms with kinetics similar to those observed for C. albicans. However, C. auris does not form hyphae, indicating distinct virulence mechanisms. Furthermore, a mutant auxotrophic for adenosine (ade2Δ) is avirulent in this model, demonstrating that the nematode can discriminate between virulent and avirulent strains. The C. elegans model also recapitulates strain-to-strain variability in virulence observed in mouse models. In addition, I have adapted a live/dead staining methodology using SYTOX Orange to enable a high-throughput assay suitable for analyzing multiple strains or genetic mutants. Finally, I used this high-throughput assay to screen an insertion mutant library for avirulent mutants and identified several potential novel virulence factors. This model has significant advantages relative to other invertebrate virulence models for C. auris and is a beneficial complement to the more challenging and variable murine models.

Advisory Committee:

• Michael Lorenz, PhD, Chair
• Catherine Denicourt, PhD
• Danielle Garsin, PhD
• Theresa Kohler, PhD
• Christian Perez, PhD
• Ambro van Hoof, PhD

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