Effect of steroids on Acanthamoeba cysts and trophozoites

PURPOSE. Topical steroids are frequently used to control corneal inflammati on and uveitis or is administered after surgery, to prevent corneal graft r ejection, This Study was undertaken to determine whether steroids could aff ect the pathogenicity of Acanthamoeba castellanii. METHODS. The effect of dexamethasone phosphate on excystment, proliferation , and encystment of trophozoites and cysts of A. castellanii was examined i n vitro. Cytolysis capacity of steroid-treated Acanthamoeba was quantified by a spectrophotometric assay, and plasminogen activators were measured by a fibrinolysis assay. The influence of steroid treatment on corneal infecti on in a Chinese hamster model of Acanthamoeba keratitis was examined in viv o. RESULTS. Treatment of Acanthamoeba cysts with dexamethasone induced 4- to 1 0-fold increases in the number of trophozoites compared with untreated cont rol cultures. Acceleration of trophozoite proliferation was observed when t rophozoites were treated with dexamethasone. However, dexamethasone treatme nt did not affect encystment of Acanthamoeba trophozoites. Dexamethasone-tr eated trophozoites or cysts induced a significant cytopathic effect on corn eal epithelial cells compared with untreated organisms. Supernatants collec ted from either dexamethasone-treated or untreated organisms failed to lyse corneal epithelial cells, Treatment of organisms with dexamethasone had no effect on production of plasminogen activators by Acanthamoeba trophozoite s. Intramuscular injection of dexamethasone had a profound effect on the in cidence, severity, and chronicity of keratitis. Keratitis in dexamethasone- treated hamsters was significantly more severe at all time points than in u ntreated animals (P < 0.05). CONCLUSIONS. These findings indicate that exposure of Acanthamoeba trophozo ites and cy,sts to dexamethasone increases the pathogenicity of the organis ms. The results emphasize the importance of maintaining adequate amebicidal therapy if a topical steroid is used in the management of Acanthamoeba ker atitis.