Drosophila melanogaster as a model to study virulence and azole treatment of the emerging pathogen Candida auris

Objectives Candida auris is an emerging, often MDR, yeast pathogen. Efficient animal models are needed to study its pathogenicity and treatment. Therefore, we developed a C. auris fruit fly infection model. Methods Toll(I-RXA)/Toll(r632) female flies were infected with 10 different C. auris strains from the CDC Antimicrobial Resistance bank panel. We used three clinical Candida albicans strains as controls. For drug protection assays, fly survival was assessed along with measurement of fungal burden (cfu/g tissue) and histopathology in C. auris-infected flies fed with fluconazole- or posaconazole-containing food. Results Despite slower in vitro growth, all 10 C. auris isolates caused significantly greater mortality than C. albicans in infected flies, with >80% of C. auris-infected flies dying by day 7 post-infection (versus 67% with C. albicans, P<0.001-0.005). Comparison of C. auris isolates from different geographical clades revealed more rapid in vitro growth of South American isolates and greater virulence in infected flies, whereas the aggregative capacity of C. auris strains had minimal impact on their growth and pathogenicity. Survival protection and decreased fungal burden of fluconazole- or posaconazole-fed flies infected with two C. auris strains were in line with the isolates' disparate in vitro azole susceptibility. High reproducibility of survival curves for both non-treated and antifungal-treated infected flies was seen, with coefficients of variation of 0.00-0.31 for 7day mortality. Conclusions Toll-deficient flies could provide a fast, reliable and inexpensive model to study pathogenesis and drug activity in C. auris candidiasis.