Differentiating E. histolytica Trophozoites from the Commensal Amoeba Trophs

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Differentiating E. histolytica Trophozoites from the Commensal Amoeba Trophs

Regarding routine microscopic methods, the permanent stained smear is the most important technique for recovering trophozoites and cysts. The chart below shows some differentiating characteristics between E. histolytica and the non-pathogenic amoebae trophozoites previously mentioned. As you can see, trophozoites are often difficult to distinguish from one another, so it is always best to base diagnoses on the cyst form, if possible.
Nuclear characteristics given are the peripheral chromatin (around the membrane of the nucleus) and the karyosome, which is the central chromatin that appears as a spot or blotch near the center
Images are of trichrome-stained organisms (not a differential stain - blue, green, and pink colors vary among structures), and sizes are given. Still, images are not relative to one another.
Table 4. Differentiating E. histolytica Trophozoites from the Commensal Amoeba Trophs.
OrganismImage NucleusCytoplasm
Entamoeba histolytica
12–60 μm (usual is 15–20 μm)

(7)
Single
Chromatin: finely granular and evenly distributed around periphery of nucleus.
Karyosome: small and central
Finely granular "ground glass" appearance
May contain bacteria or RBC's
E. coli
15–50 μm (usual is 20–25 μm)

(8)
Single
Chromatin: clumped and uneven around periphery
Karyosome: large, may be diffuse, may be eccentric or central
Granular
Usually vacuolated
Can contain bacteria, yeast and other debris
E. hartmanni
5–12 μm (usual 8–10 μm)

(9)
Single
Chromatin: even, may appear as a solid ring
Karyosome: small and compact; central or eccentric
Finely granular
Endolimax nana
6–12 μm

(10)
Single
Chromatin: no peripheral chromatin usually seen
Karyosome: large and blot-like, may take up a large portion of the nucleus
Granular, may be vacuolated
Iodamoeba butschlii
8–20 μm (usual 12–15 μm)

(11)
Single
Chromatin: usually no peripheral chromatin
Karyosome: large (occasionally surrounded by refractile granules)
Granular; may be vacuolated
7. Walkowski, S. (2012). Entamoeba histolytica trophozoite. Wikimedia Commons.https://commons.wikimedia.org/w/index.php?curid=24557823
8. Yasser. (2008). Entamoeba coli trophozoite. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Entamoeba_Coli_trophozoite.jpg
9. Osman, I. (2012). Entamoeba hartmani: Amoebic infections in humans." Wikimedia Commons. https://commons.wikimedia.org/w/index.php?curid=33628181
10. Centers for Disease Control and Prevention. (2018). Morphological identification of the commensal protozoa of the human intestinal tract Webinar: Endolimax nana. Wikimedia Commons.https://commons.wikimedia.org/wiki/File:Morphological_Identification_of_the_Commensal_Protozoa_of_the_Human_Intestinal_Tract.webm
11. Centers for Disease Control and Prevention. (2019). Intestinal (non-pathogenic) amebae - Figure A: Trophozoite of I. buetschlii stained with trichrome. CDC.gov. https://www.cdc.gov/dpdx/intestinalamebae/index.html