TABLE 1.

Morphologic features and pathogenicity of intestinal amebae^a

Characteristics	E. histolytica, E. dispar and E. moshkovskiib	E. hartmanni	E. coli	E. polecki	D. fragilisc	E. nana	I. bütschlii
Trophozoites (size, nucleus, and movement)	15-20 μm; 1 nucleus; actively motile cytoplasmic protrusions, quickly finger shaped pseudopodium	8-10 μm; 1 nucleus; nonsuccessive	20-25 μm; 1 nucleus; slow movement, short and blunt pseudopodium	15-20 μm; 1 nucleus; motility resembles E. coli	7-12 μm; mono- and binucleate; pseudopoedium hyaline broad leaflike serrated margins successive motility	7-9 μm; 1 nucleus, blunt and hyaline pseudoodium, slow movements	9-14 μm; 1 nucleus, slow movement, nonsuccessive, hyaline pseudopodium
Cysts (size, nucleus)	12-15 μm; mature cyst has 4 nuclei, immature cyst has 1 or 2 nuclei	6-8 μm; mature cyst has 4 nuclei; immature cyst has 1 or 2 nuclei; 2 nucleated cysts very common	15-25 μm; mature cyst has 8 nuclei, rarely 16 or more nuclei	10-15 μm; 1 nucleus, very rarely binucleate or quadrinucleate	No cyst stage	6-8 μm; 4 nuclei	10-12 μm; 1 nucleus
Appearance of trophozoites	Stained trophozoites fine, uniform granules of peripheral chromatin, and small central karyosome in nucleus; ingested RBC (E. dispar and E. moshkovskii are similar to E. histolytica trophozoites, sometimes ingested RBCs)	Nuclear structure similar to E. histolytica; ingested bacteria; cytoplasm finely granular	Nuclear with irregular cluster of peripheral chromatin; large, irregular, eccentric karyosome	Nucleus with minute central karyosome, with fine granules of peripheral chromatin, finely granular cytoplasm; ingested bacteria	High percentage of binucleate trophozoites; nuclei without peripheral chromatin	Nucleus with large karyosome; no peripheral chromatin	Large central karyosom, granular cytoplasm
Appearance of cysts	Uniform size in having both karyosome and peripheral chromatin, typical nuclear structure, chromatodial bars with squared or rounded ends	Typical nuclear structure, chromatodial bars with rounded or squared ends	Typical nuclear structure, sliver-shaped or irregular chromatoidals	Mononucleate; large central karyosome; inclusion masses, chromatoid bars with pointed or angular ends	No cyst stage	Chromatin, 4 nuclei with large karyosomes and no peripheral chromatin	Large karyosome, eccentric refractile granules (basket nucleus), large compact glycogen, no peripheral chromatin
Pathogenicity	Pathogen (E. dispar and E. moshkovskii are nonpathogens)	Nonpathogen	Nonpathogen	Nonpathogen	Nonpathogen	Nonpathogen	Nonpathogen

^aData from references 40, 64, 65, 80, and 116.

^bE. moshkovskii is present in free-living protozoa.

^cD. fragilis is a flagellate but resembles organisms within the amebae.