1726. Candida albicans Virulence Genes Induced During Intra-abdominal Candidiasis (IAC) in the Absence of Antifungal Exposure Mediate Echinocandin Resistance

BACKGROUND: We developed and validated a mouse model of C. albicans IAC that mimics peritonitis and abscesses (IAA) in humans, and that is amenable to temporal–spatial transcriptional profiling and virulence studies. METHODS: We measured C. albicans SC5314 gene expression by RNA-Seq (RiboPure extraction; Illumina MiSeq) in triplicate during early peritonitis (within 30 minutes of infection), late peritonitis (24 hours) and IAA (48 hours). Differential expression was defined by ≥2-fold differences at false discovery rate ≤0.01. RESULTS: ≥7 million C. albicans reads were detected in each experiment. 67% of C. albicans reads mapped to coding sequences, covering 93% of open reading frames. The 50 C. albicans genes most highly expressed during early peritonitis were associated with pH (including RIM101 and PHR1) and oxidative stress responses, and adhesion/hyphal growth (e.g., ALS3, HWP1, ECM331, SAP6). The corresponding 50 C. albicans late peritonitis genes were associated with neutrophil/macrophage responses and nutrient acquisition (glyoxylate cycle, fatty acid β-oxidation, iron homeostasis). Responses within IAA included DNA damage and iron metabolism, reflecting stress response and nutrient/metal limitation. The top 50 core gene responses for all stages were associated with adhesion, stress response, and glucose transport. Among the most up-regulated genes in late peritonitis and IAA compared with early peritonitis were those involved antifungal drug resistance (CDR family, MDR1, FLU1, and ERG family), although mice were not exposed to antifungals. Null and reconstitution mutants for genes involved in adhesion (ALS3), copper transport (CCC2), DNA (DDI1) and cell wall damage responses (DAP1 homologs), and glycerol biosynthesis (RHR2) were attenuated for virulence in temporal-spatial fashion during peritonitis and IAA, and/or hyper-susceptible to phagocytosis and echinocandins (table). CONCLUSION: C. albicans relies upon diverse biologic processes to cause peritonitis and IAA. Multiple genes induced in response to stress during IAC mediate virulence, phagocyte, and echinocandin resistance. Therefore, pathogenic strategies used by C. albicans during IAC may lessen responses to echinocandin treatment, even in the absence of drug exposure or FKS mutations. [Image: see text] DISCLOSURES: All authors: No reported disclosures.