Differences in virulence between two Candida albicans strains in experimental keratitis

PURPOSE. To study the differences in disease caused by two wild-type strain s of Candida albicans in a model of contact lens-facilitated keratitis in r abbits. METHODS. Two strains, SC5314 and VE175, were examined. Standardized inocula were placed on the debrided corneal surface of one eye in Dutch belted rab bits and covered with a contact lens. A temporary tarsorrhaphy was opened a fter 24 hours with removal of the contact lens. Six days later, corneas wer e photographed and animals killed. Corneas were bisected with one half for quantitative isolate recovery and the other for stromal penetration by hyph ae. RESULTS. Strain SC5314 was significantly more virulent. The mean hyphal pen etration into the cornea was 24.4% +/- 8.5% of the corneal thickness, and i n three of six corneas hyphae penetrated through the entire cornea. In cont rast, for VE175, the mean hyphal penetration was 2.6% +/- 1.2%. The differe nce between these two strains was statistically significant (P = 0.0297). H yphae did not penetrate into the deep layers of the cornea in any of the si x rabbits infected with VE175. The grading of clinical disease was consiste nt with histology, in that strain SC5314 caused more severe infection than VE175 and the difference was statistically significant (P = 0.0048). There was no difference in isolate recovery. CONCLUSIONS. Wild-type strains of C albicans can differ significantly in vi rulence as measured by depth of fungal invasion into corneas and clinical e valuation of infection. Further characterization of the intrinsic genetic d ifferences between such strains may help identify factors responsible for f ungal virulence.