Experimental Keratomycosis in a Mouse Model

Abstract

PURPOSE: To establish a murine model of corneal candidiasis that permits molecular evaluation of fungal adherence and invasion. METHODS: Corneas of immunocompetent, methylprednisolone-treated, and cyclophosphamide-treated adult NIH Swiss and BALB/c mice were topically mock inoculated or inoculated with 10-fold increasing amounts between 100 and 100 million colony-forming units (CFU) of Candida albicans after unilateral corneal scarification. Mock-inoculated eyes served as the control. Eyes were scored daily on a 12-point scale to categorize corneal inflammation and were enucleated for quantitative fungal cultures, analysis by polymerase chain reaction (PCR), and histopathologic examination. RESULTS: At least 100 CFU of C. albicans initiated measurable corneal infection, but 1 million or more colony-forming units were needed to induce consistent keratitis. Treatment with methylprednisolone increased disease severity in infected BALB/c mice and fungal persistence in both BALB/c and NIH Swiss mice. Treatment with cyclophosphamide increased disease severity and fungal persistence in both strains of mice. Infectious organisms were recovered by quantitative culture, and candidal DNA was detectable by PCR. C. albicans, inflammatory cells, and stromal necrosis were histologically evident within ocular tissue. CONCLUSIONS: Although mice are innately resistant to Candida infection after corneal inoculation, moderate to severe keratomycosis can be established in immunocompromised mice by the route of corneal scarification. Although differences between mouse strains and among immunosuppressive regimens remain to be explored, this murine model provides the basis for understanding the pathogenesis of fungal infections of the cornea.