The presence of ingested red blood cells may be seen in the trophozoite of which organism?

• A. Giardia duodenalis
• B. Entamoeba histolytica
• C. Dientamoeba fragilis
• D. Entamoeba coli

Answer: (B)

Ingestion of red blood cells by the trophozoite is a hallmark feature of Entamoeba histolytica. When these trophozoites invade the colonic mucosa, they phagocytose host cells, and red blood cells can be seen inside the cytoplasm on stained preparations. This erythrophagocytosis helps distinguish E. histolytica from other intestinal amoebae, which do not typically ingest red blood cells.

Giardia duodenalis trophozoites reside in the small intestine and do not show erythrophagocytosis; Dientamoeba fragilis and Entamoeba coli may resemble some features of E. histolytica but do not characteristically contain ingested red blood cells in their trophozoites.