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Table 3
Differential
Morphology of Protozoa Found in Stool Specimens of
Humans: Amoebae-Trophozoites
NUCLEUS |
CYTOPLASM |
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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 granular. | Red blood cells occasionally. Noninvasive organisms may contain bacteria. |
| Entamoeba hartmanni | 5-12mm. 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 | 15-50mm. 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 | 10-25mm. 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, granular. | 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 contain red blood cells.
3Flagellate - included with amoebae for diagnostic
purposes.
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