2887. Identifying Candida albicans Transcription Factors (TFs) That Regulate Pathogenesis of Intra-abdominal Candidiasis (IAC) by Screening a Deletion Mutant Library

BACKGROUND: IAC is a common manifestation of invasive candidiasis, but its pathogenesis is poorly understood. We developed a mouse model of C. albicans IAC, in which disease progresses from peritonitis to abscesses (IAA) in a manner that recapitulates human infection. Our goal was to use the model to identify C. albicans TFs that regulate virulence during IAC. METHODS: We screened a signature-tagged library (48 unique oligonucleotide markers) of homozygous deletion mutants for 165 C. albicans TF genes, created in duplicate in strain SC5314 (S. Noble). Mice were infected intra-peritoneally in triplicate with pools of 24 mutants and wild-type, and strains harvested at 72 hours in IAA. RESULTS: Twenty-one TF mutants were significantly attenuated for virulence in both libraries, and 2 TF mutants were significantly more virulent in both libraries, as measured by tissue burdens (figure). Biologic processes over-represented among attenuated mutants were regulation of pH responses, biofilm, hyphal formation, echinocandin responses, and copper metabolism. pH responses are likely to be crucial to pathogenesis of IAC, as C. albicans transitions from pH 8 during peritonitis to pH 6.8 within IAA. 9 pH response regulators contributing to virulence included RIM101, STP2 (alkaline), ASH1, SFL1, SFL2 (neutral), MNL1, SKO1, PHO4 (weak acid), and CSR1 (acid). We created rim101 null mutant and reconstitution strains, and demonstrated that the gene was essential for complete virulence during peritonitis and IAA. Transcriptional profiling of strains by RT-PCR during peritonitis and in vitro showed both conserved and rewired Rim101 targets. SAP5, which encodes an aspartyl protease, is a major Rim101 target in vivo and in vitro; over-expression of SAP5 in rim101 restored virulence during IAA at 3, 7, and 10 days, but not during peritonitis. Other pH regulatory TF genes are currently being validated as virulence determinants, and pathway relationships between MNL1, SKO1, and PHO4 during IAA formation are being explored through epistasis approaches. CONCLUSION: Screening of a C. albicans TF mutant library identified pH responses and other biologic processes as important during pathogenesis of IAC. Rim101, an alkaline pH response regulator, contributes to both peritonitis and IAA, the latter at least in part through its effects on Sap5. [Image: see text] DISCLOSURES: All Authors: No reported Disclosures.