Which method distinguishes Entamoeba histolytica from Entamoeba dispar using immunologic assays?

• A. Number of nuclei
• B. Size of the cyst
• C. Shape and location of the karyosome and peripheral chromatin
• D. Distinguishing surface antigens by immunologic assays

Answer: (D)

The method relies on detecting species-specific antigens rather than relying on how the organism looks under a microscope. Entamoeba histolytica and Entamoeba dispar appear identical when you examine cysts or trophozoites, so features like the number of nuclei, cyst size, or the shape and arrangement of the karyosome and peripheral chromatin cannot separate them. Immunologic assays, however, target surface antigens that are unique to E. histolytica. Using antibodies that bind these specific antigens lets you identify the pathogenic species in a sample, distinguishing it from E. dispar. Therefore, antigen-detection immunologic assays are the appropriate method for differentiation.