In diagnosing Entamoeba histolytica dysentery, which microscopic finding in a freshly passed stool definitively confirms active amoebiasis (as opposed to non-pathogenic carriage)?

• A Trophozoites containing ingested red blood cells (erythrophagocytosis) ✓
• B Presence of cysts with 4 nuclei
• C Cysts with chromatoid bars
• D Trophozoites without ingested erythrocytes

Explanation

Trophozoites of E. histolytica containing ingested erythrocytes (haematophagous trophozoites or 'magna forms') are the definitive marker of active invasive amoebiasis, distinguishing it from non-pathogenic E. dispar, which is morphologically identical but never ingests red blood cells. Cysts with four nuclei and chromatoid bars are features common to both E. histolytica and E. dispar and cannot be used to confirm pathogenicity. Trophozoites without erythrocytes cannot be distinguished from E. dispar morphologically.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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