Virulence of extracellular phospholipase B of Candida albicans in rabbit experimental keratomycosis

Abstract

To determine the virulence of extracellular phospholipase B (PLB) of Candida albicans in experimental keratomycosis. It was an experimental study. The PLB-deficient mutant strain of Candida albicans and its isogenic parental strain were used in this study. The effects of these two strains on the model of experimental keratomycosis in 48 New Zealand albino rabbits covered with contact lens was compared by observing the dynamic changes clinically and histopathologically. In vitro, these two strains were incubated with the corneal stromal cells separately (37 degrees C, 5% CO2). The influence of these two strains on monolayer keratocytes were detected by scanning electron microscopy (SEM), enzyme linked immunosorbent assay (ELISA), and flow cytometry with Annexin V/propidium iodide. The hyphae of these two strains grew perpendicularly to the corneal stromal lamellae. The difference of the hyphal invasion inoculated for 2 days by these two isogenic strains was statistically significant (P = 0.002), but at other intervals, no significant difference was found. The severity of the inflammation in parental keratomycosis was the same as that in PLB null strain at any time points (P > 0.05). Under SEM, the morphogenesis and the number of adherent germ tubes of these two isogenic strains appeared similarly (P > 0.05), but the number of germ tubes penetrating cell monolayer was significantly different (P = 0.009). Obviously more prostaglandin E2 (PGE2) was detected in the culture supernatants of parental strain group (65,466 +/- 5773) pg/ml than that of the null strain group (18,025 +/- 5232) pg/ml. The percentages of the cells with damaged cellular membrane in the parental group, the PLB null group and the control group, were 3.02%, 2.04% and 0.12%, respectively. The percentages of apoptosis cells in these three groups were 33.17%, 27.56% and 1.46%, respectively. The percentages of living cells were 63.81%, 70.40% and 98.41%, respectively. PLB shows virulent effects in triggering fungal invasion in cornea immediately following fungal adherence by decomposing membrane phospholipids and leading to cell lysis. However, its virulent effect does not appear to be critical as in the hematogenous model of disseminated candidiasis.