[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 3 The Amebas
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Cytoplasm
Eccentric
karyosome
Uneven peripheral
chromatin
A
Cyst wall
Size range: 8-35 m
Average size: 12-25 m
Chromatoid bars
B
FIGURE 3-11 A, Entamoeba coli cyst. B, Entamoeba coli cyst with five nuclei visible (trichome stain, ×). (B from
Mahon CR, Lehman DC, Manuselis G: Textbook of diagnostic microbiology, ed 4, St Louis, 2011, Saunders.)
TABLE 3-6
Entamoeba coli Cyst: Typical
Characteristics at a Glance
Parameter Description
Size range 8-35 µm
Shape
Round to spherical
Number of nuclei One to eight
Karyosome Large, irregular shape, eccentric
Peripheral Unevenly distributed
chromatin
Cytoplasm Coarse and granulated
Cytoplasmic Diffuse glycogen mass present in
inclusions young cysts; may displace nuclei
(often seen in cysts with two
nuclei) to opposite ends of
the cyst
Thin chromatoid bars with pointed
to splintered ends in young cysts
nuclei present to opposite ends of the cyst, a
variation often seen in cysts with two nuclei
present. Thin chromatoid bars, often with
pointed to splintered ends, may also be contained
in the cytoplasm of young cysts.
Laboratory Diagnosis
Stool examination is the method of choice for
the recovery of E. coli trophozoites and cysts.
Although not considered as being pathogenic,
the presence of E. coli suggests ingestion of contaminated
food or drink. Laboratory technicians
should therefore examine these preparations
carefully for the presence of pathogenic parasites
in addition to the nonpathogenic E. coli.