Cytotoxicity of a cell free extract of Entamoeba histolytica

Previous attempts to demonstrate toxicity of cell-free extracts prepared from axenically cultivated E. histolytica have proved unsuccessful. We report here the successful production of cytopathic effect by cell-free extracts of two strains (HM-1 and HK-9) of E. histolytica in tissue culture monolayers. The cytotoxic effect demonstrated was sensitive to serum in the assay medium. Failure of past investigations to demonstrate cytotoxic activity may be explained by the presence of serum in the assay systems used.