Stool microscopy from a patient with bloody dysentery shows trophozoites ingesting erythrocytes. The trophozoites measure 20–40 µm with a finely granular cytoplasm and a single nucleus with central karyosome. Serology for antibodies to Entamoeba is positive. Which test best distinguishes E. histolytica from E. dispar in a reference laboratory?
- A Enzyme-linked immunosorbent assay (ELISA) for Gal/GalNAc lectin antigen ✓
- B Stool culture on Robinson's medium
- C Stool microscopy of fresh sample
- D String test (Enterotest)
Explanation
Morphologically, E. histolytica and E. dispar are indistinguishable on standard microscopy. The ELISA detecting the species-specific Gal/GalNAc (galactose/N-acetyl-D-galactosamine) lectin antigen of E. histolytica is the recommended molecular/antigen method for differentiation; PCR targeting the species-specific gene is the gold standard. E. dispar is non-pathogenic and does not produce the same surface lectin. Stool culture on Robinson's medium can grow trophozoites but cannot reliably distinguish species. The string test is used for detecting Giardia and Strongyloides, not Entamoeba.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.