The microscopic image above shows a trophozoite with characteristic features. This finding is most consistent with:

Explanation

## Image Findings * A relatively large, irregularly shaped amoeboid cell (trophozoite). * Presence of a single, distinct nucleus with a **small, centrally located karyosome**. * **Fine, evenly distributed peripheral chromatin** along the nuclear membrane. * Cytoplasm contains multiple **ingested red blood cells** (dark red, spherical structures). * A broad, finger-like pseudopod is visible, indicating motility. ## Diagnosis **Key Point:** The presence of ingested red blood cells within the cytoplasm of an amoeboid trophozoite, combined with a single nucleus having a small central karyosome and fine peripheral chromatin, is **pathognomonic for *Entamoeba histolytica* trophozoite**. *Entamoeba histolytica* is the causative agent of amoebiasis, which can manifest as amoebic dysentery (characterized by bloody diarrhea due to colonic ulceration) and extraintestinal amoebiasis, most commonly amoebic liver abscess. The ingestion of red blood cells is a crucial diagnostic feature, reflecting its invasive nature. ## Differential Diagnosis | Feature | *Entamoeba histolytica* trophozoite | *Entamoeba coli* trophozoite | *Giardia lamblia* trophozoite | *Balantidium coli* trophozoite | |---------------------|-------------------------------------|------------------------------------|------------------------------------|--------------------------------| | Size | 15-60 µm | 15-50 µm | 10-20 µm | 50-100 µm | | Nuclei | 1 (small, central karyosome) | 1 (large, eccentric karyosome) | 2 (oval, anterior) | 1 macronucleus (kidney-shaped), 1 micronucleus | | Ingested RBCs | **Common and diagnostic** | Rare | Absent | Absent | | Motility | Unidirectional, progressive | Sluggish, non-progressive | Falling leaf motility (flagella) | Rapid, rotatory (cilia) | | Shape | Amoeboid | Amoeboid | Pear-shaped | Ovoid | ## Clinical Relevance **Clinical Pearl:** *Entamoeba histolytica* causes amoebic dysentery, characterized by **flask-shaped ulcers** in the colon and can lead to complications like **amoebic liver abscess**. Early diagnosis through stool microscopy or antigen detection is crucial for effective treatment. ## High-Yield for NEET PG **High-Yield:** **Ingestion of red blood cells by a trophozoite is the most reliable morphological feature to differentiate *Entamoeba histolytica* from non-pathogenic amoebae like *Entamoeba coli***. **Key Point:** The nuclear morphology (small, central karyosome, fine peripheral chromatin) is also important but can be harder to discern in routine stains compared to ingested RBCs. ## Mnemonic **Mnemonic:** "**H**istolytica **H**as **H**emoglobin" (referring to ingested RBCs). ## Common Traps **Warning:** Differentiating *E. histolytica* from *E. coli* is a common trap. Always look for ingested RBCs and the characteristic nuclear features. *E. coli* trophozoites typically have a larger, eccentric karyosome and coarse, irregular peripheral chromatin, and rarely ingest RBCs. ## Reference [cite:Ananthanarayan & Paniker's Textbook of Microbiology, 10th Ed, Ch 70]