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Establishment of a Candida albicans Infection Model in Caenorhabditis elegans for Study of Fungal Pathogenesis
Background: Candida albicans is an opportunistic fungal pathogen that can cause life-threatening infections in immunocompromised individuals. Due to ethical and budgetary concerns associated with the use of vertebrate animals in research, interest in alternative models has increased over the past several decades. Caenorhabditis elegans, a non-parasitic nematode, has emerged as an attractive invertebrate model host due to its ease of maintenance and propagation, short life cycle, and susceptibility to a wide range of human pathogens. C. elegans relies solely on its innate immune system to mount antifungal defenses, many of which are evolutionarily conserved elements that have mammalian orthologs. The focus of our study was to design a C. elegans infection model using C. albicans yeast. Methods: Synchronized larval stage 4 worms were challenged with various doses of live C. albicans yeast cells for 4 hours at 20°C and 30°C. Survival of the worms was monitored every 24 hours for 5 days post-challenge. Some of the worms (n=416) at 24 hours post-challenge were homogenized, and homogenates plated on Sabouraud's agar for determination of fungal burden. Results: Fungal burden assessment showed an average of 380 colony forming units per worm at 24 hours post-challenge with 5x10^6 viable yeast cells/mL in PBS at 30°C. At 120 hours post-challenge, the infection resulted in 5% and 95% survival of infected and control groups, respectively. In future studies, we will use this model to investigate C. elegans innate immune responses following infection and in response to antifungal drugs and various immune adjuvants.