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Background 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. In the present study, we developed a Candida albicans quantitative infection model in Caenorhabditis elegans, a nonparasitic invertebrate nematode, to test the antifungal effects of liposomal amphotericin B (L-AmB). Methods To establish a lethal C. albicans infection, larval Stage 4 worms [n = 30/group (gp)] were fed various doses of yeast (2.5 × 102–2.5 × 105 cells/gp) for 4 hours at 20°C or 30°C. The infection was evaluated by monitoring worms for mortality and determining fungal burden in worm homogenates by plating for colony forming units every 24 hours for 4 days post-challenge. To examine the worm’s ability to ingest L-AmB and to determine drug toxicity, uninfected worms were fed L-AmB (6.3–25 μg/gp) for 4 hours at 30°C, and drug toxicity evaluated by survival with drug concentrations determined by bioassay of worm homogenates. The lack of toxicity allowed us to evaluate L-AmB activity in worms challenged for 4 hours at 30°C with 2.5 × 105 yeast cells/gp and then treated with L-AmB (0.5–25 ug/gp) for 4 hours at 30°C, with survival rate and fungal burden to assess L-AmB treatment. Results Calbicans infection was established in worms challenged with all yeast doses, with optimum infection observed with 2.5 × 105 yeast cells/gp at 30°C (13% survival in-infected worms vs. 87% in uninfected worms). We observed that uninfected worms could take up L-AmB at doses of 6.3–25 μg/gp and yet was not toxic for the worms (93–95% survival). In worms exposed to yeast and treated with L-AmB, complete clearance of infection was achieved with the higher doses (6.3–25 μg/gp), while lower doses (1.6–3.1 μg/gp) significantly reduced the fungal burden (P ≤ 0.05). Infected worms, not treated with L-AmB had only 10% survival, while L-AmB improved survival in a dose-dependent manner giving 40% survival for 0.5 μg L-AmBi/gp and 100% survival for doses of 6.3 μg/gp and higher. Conclusion By using fungal burden as a readout of efficacy, along with survival, we have established a quantitative, reproducible, flexible method for examining the activity of L-AmB in C. elegans which could be expanded for use in evaluating other antifungal drugs and different pathogenic fungi. Disclosures All authors: No reported disclosures.

626. An Inexpensive Quantitative Method for Testing Anti-Fungal Drug Activity Using the Invertebrate Caenorhabditis elegans