Morphology - Table 3

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Table 3
Differential Morphology of Protozoa Found in Stool Specimens of Humans: Amebae-Trophozoites

			Nucleus			Cytoplasm
Species	Size (Length)	Motility	Number	Peripheral Chromatin	Karyosomal Chromatin	Appearance	Inclusions
Entamoeba histolytica	10-60 mm. Usual range, 15-20 mm commensal form.¹ Over 20 mm invasive form.²	Progressive with hyaline, finger- like pseudopods.	1 Not visible in unstained preparations.	Fine granules. Usually evenly distributed and uniform in size.	Small, discrete. Usually centrally located, but occasionally is eccentric.	Finely qranular.	Red blood cells occasionally. Noninvasive organisms may contain bacteria.
Entamoeba hartmanni	5-12 mm. Usual range, 8-10 mm.	Usually nonprogressive but may be progressive occasionally.	1 Not visible in unstained preparations.	Similar to E. histolytica.	Small, discrete, often eccentric.	Finely granular.	Bacteria.
Entamoeba coli	15-50 mm. Usual range, 20-25 mm.	Sluggish, nonprogressive, with blunt pseudopods.	1 Often visible in unstained preparations.	Coarse granules, irregular in size and distribution.	Large, discrete, usually eccentric.	Coarse, often vacuolated.	Bacteria, yeasts, other materials.
Entamoeba polecki	10-25 mm. Usual range, 15-20 mm.	Usually sluggish, similar to E. coli. Occasionally, in diarrheic specimens, motility may be progressive.	1 May be slightly visible in unstained preparations. Occasionally may be irregularly distorted by pressure from vacuoles in cytoplasm.	Usually fine granules evenly distributed. Occasionally granules may be irregularly arranged. Chromatin sometimes in plaques or crescents.	Small, discrete, eccentric. Occasionally large, diffuse or irregular.	Coarsely, granular, may resemble E. coli. Contains numerous vacuoles.	Bacteria, yeasts.
Endolimax nana	6-12 mm. Usual range, 8-10 mm.	Sluggish, usually nonprogressive with blunt pseudopods.	1 Visible occasionally in unstained preparations.	None.	Large, irregularly shaped, blot-like.	Granular, vacuolated.	Bacteria.
Iodamoeba buetschlii	8-20 mm. Usual range, 12-15 mm.	Sluggish, usually nonprogressive.	1 Not usually visible in unstained preparations.	None.	Large, usually central. Surrounded by refractile, achromatic granules. These granules are often not distinct even in stained slides.	Coarsely granular, vacuolated.	Bacteria, yeasts, or other material.
Dientamoeba fragilis³	5-15 mm. Usual range, 9-12 mm.	Pseudopods are angular, serrated, or broad lobed, and hyaline, almost transparent.	2 (In approximately 20% of organisms only 1 nucleus is present.) Nuclei invisible in unstained preparations.	None.	Large cluster of 4-8 granules.	Finely, qranular.	Bacteria: occasionally red blood cells.

¹Commensal form: usually found in asymptomatic or chronic cases; may contain bacteria.
²Invasive form: usually found in acute cases: often remain red blood cells.
³Flagellate: included with amebae for diagnostic purposes.

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