TABLE 1.

Characteristics of trophozoites and cysts of common intestinal Entamoeba speciesa

CharacteristicsE. histolytica/E. dispar/ E. moshkovskiiE. hartmanniE. coliE. polecki
Size, nuclei, and motility
    Trophozoites15-20 μm, 1 nucleus (difficult to see in unstained preparations), actively motile with finger shaped pseudopodia8-10 μm, 1 nucleus (usually not seen in unstained prepn), usually unprogressive20-25 μm, 1 nucleus (often visible in unstained prepn); sluggish, short, and blunt pseudopodia15-20 μm, 1 nucleus (occasionally seen on wet prepn), sluggish
    Cysts10-15 μm, mature cyst with 4 nuclei, immature cyst has 1 or 2 nuclei (nuclear characters difficult to see on wet prepn)6-8 μm, mature cyst with 4 nuclei, immature cyst has 1 or 2 nuclei, two nucleated cysts very common15-25 μm, mature cyst has 8 nuclei, occasionally 16 or more nuclei10-15 μm, mature cyst with 1 nucleus, rarely 2 or 4 nuclei
Other features
    Trophozoites
        Chromatin (stained)Chromatin peripheral, may have beaded appearanceNucleus may stain more darkly than E. histolytica, chromatin may appear as solid ring rather than beaded (trichrome)Chromatin clumped and unevenly arranged, appears as solid ring with no beadsChromatin finely granular, chromatin may also be clumped at one or both edges of membrane
        Karyosome (stained)Karyosome small, compact, centrally located but may be eccentricKaryosome usually small and compact; centrally located or eccentricKaryosome large, not compact, may or may not be eccentric, may be diffuse or darkly stainedKaryosome small and usually centrally located
        Cytoplasm (stained)Cytoplasm is fine, granular, may contain bacteria; presence of RBCs diagnostic for E. histolytica, although some E. dispar strains may very occasionally contain RBCsCytoplasm finely granular, may contain bacteria, no RBCsCytoplasm granular with differentiation into cytoplasm and endoplasm, vacuolated; bacteria, yeast, and other debris may be presentCytoplasm is finely granular, may contain ingested bacteria
    Cysts
        Chromatin (stained)Chromatin peripheral with fine uniform granules, evenly distributedChromatin granules evenly distributed (nuclear characteristics may be difficult to see)Chromatin coarsely granular, may be clumped and unevenly arrangedChromatin finely granular
        Karyosome (stained)Karyosome is small, compact, usually centrally located but occasionally eccentricKaryosome is small, compact, usually centrally locatedKaryosome large, eccentric, occasionally centrally locatedKaryosome small and usually centrally located
        Cytoplasm (stained)May be present; chromatoidal bodies usually elongate with blunt, rounded, smooth edges; may be round or oval; chromatin may be diffuse or absent in mature cyst; clumped chromatin mass may be present in early cystsUsually present; chromatoidal bodies usually elongate with blunt, rounded, smooth edges; may be round or oval; chromatin may or may not be presentMay be present (less frequent than in E. histolytica), splinter shaped with rough pointed ends, may be diffuse or absent in mature cysts, clumped mass occasionally seen in mature cystsAbundant chromatoidal bodies with angular pointed ends, thread-like chromatoidal bodies may also be present, half of the cysts contain spherical or ovoidal inclusion mass
  • a Data are from references 57, 73, and 188.