400 Genetic heterogeneity and antifungal resistance within Candida infecting populations

Objectives/Goals: This study will assess population heterogeneity in Candida bloodstream infections by quantifying antifungal resistance, fitness, and genomic diversity to understand clonality and develop a high-throughput screening tool to detect population-level resistance to update clinical practice. Methods/Study Population: This study assesses antifungal resistance and population heterogeneity in Candida bloodstream isolates collected through multiple Midwest hospitals. Blood samples are plated to isolate single colonies and population samples, which are then archived. We test resistance to key antifungals using EUCAST guidelines, conduct growth curve assays, and perform whole-genome sequencing to determine genetic diversity. A high-throughput screening method tracks colony growth under different drug conditions using time-lapse imaging and custom analysis software. The findings will reveal the extent of antifungal resistance and genetic variation within infecting populations, informing better clinical management. Results/Anticipated Results: Preliminary analysis of Candida glabrata bloodstream isolates show significant heterogeneity in colony morphology, antifungal resistance, and fitness. Some single colonies exhibit higher minimum inhibitory concentration values for micafungin and fluconazole than the overall population, while others show reduced susceptibility to amphotericin B, highlighting diverse resistance profiles. Growth assays reveal distinct fitness phenotypes within these populations. This variation underscores the limitations of single-colony testing and suggests a need for population-level resistance screening. We anticipate genomic analyses will identify genetic diversity underlying these differences, supporting a more comprehensive clinical approach to treatment. Discussion/Significance of Impact: This study reveals notable intrapopulation heterogeneity in Candida glabrata , including variations in colony morphology, antifungal resistance, and fitness. Findings highlight genomic diversity, introduce a novel screening method for resistance, and emphasize the need for population-level testing in clinical practice.