Purpose: To evaluate virulence in a murine keratitis model using Candida albicans homozygous mutants deficient in one or more secreted aspartyl proteinases encoded by SAP genes or in transcriptional factors encoded by EFG1 and CPH1 genes.
Methods: Corneas of BALB/c mice were scarified and topically inoculated with 10(6) colony-forming units of a C. albicans human isolate (SC5314), triple SAP-null mutants (SAP1-3(-/-) and SAP4-6(-/-)), double mutants (SAP4/5(-/-), SAP4/6(-/-), SAP5/6(-/-), and SAP9/10(-/-) and EFG1(-/-)/CPH1(-/-)), single mutants (SAP4(-/-), SAP5(-/-) and SAP6(-/-), EFG1(-/-), and CPH1(-/-)), SAP6 rescuant, or parental controls (CAF2-1 and CAI-4). Animals were evaluated daily for up to 8 days after inoculation.
Results: Wild-type C. albicans induced severe, sustained ulcerative keratitis, and the fungal strains (CAF2-1 and CAI-4) used to generate mutants had similar corneal pathogenicity. SAP1-3(-/-), SAP4/5(-/-), and SAP9/10(-/-) mutants produced moderate keratitis similar to the virulent parental strain. SAP4-6(-/-), SAP4/6(-/-), and SAP5/6(-/-) gave rise to significantly less severe corneal inflammation. The SAP6(-/-) single mutant resulted in mild nonulcerative keratitis that resolved spontaneously within 5 days, and the SAP6 rescuant reestablished moderate disease severity. The EFG1(-/-)/CPH1(-/-) and EFG1(-/-) mutants had reduced corneal virulence, but the CPH1(-/-) strain resulted in persistent keratitis similar to control corneas.
Conclusions: The EFG1-regulated SAP6 gene of C. albicans encodes a unique secreted aspartyl proteinase that contributes to corneal pathogenicity. The role of SAP6 during corneal infection appears to be associated with the morphogenic transformation of C. albicans yeasts into invasive filamentous forms.