[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 3 The Amebas
Pseudopod
Vacuole containing
bacteria
Eccentric
karyosome
Cytoplasm
Uneven peripheral
chromatin
A
Size range: 12-55 m
Average size: 18-27 m
FIGURE 3-9 A, Entamoeba coli trophozoite. B, Entamoeba coli trophozoite. (B from Forbes BA, Sahm DF, Weissfeld AS:
Bailey & Scott’s diagnostic microbiology, ed 12, St Louis, 2007, Mosby.)
B
FIGURE 3-10 Entamoeba coli trophozoite showing a
prominent pseudopod (arrow). Note irregular nuclear
perimeter and atypical central karyosome (iron hematoxylin
stain, ×1000). (Courtesy of WARD’S Natural Science
Establishment, Rochester, NY; http://wardsci.com.)
nucleus is easily recognizable. In unstained preparations,
the karyosome and surrounding
peripheral chromatin appear as refractile structures.
The nuclear structures are enhanced when
the trophozoites are stained. The typical nucleus
consists of a large, often irregularly shaped
karyosome that is eccentrically located. The
karyosome is surrounded by unevenly distributed
peripheral chromatin that varies in size and
becomes apparent with addition of stain. In
some cases, chromatin granules may be visible
in the area between the karyosome and peripheral
chromatin. Nuclear variations similar to
those of E. histolytica and E. hartmanni may
also occur in the trophozoites of E. coli. Vacuoles,
often containing bacteria, are commonly
seen in the coarsely granulated cytoplasm. In
contrast to E. histolytica, red blood cell inclusions
are not present in the trophozoites of
E. coli.
Cysts. The cysts of E. coli vary in size from
8 to 35 µm and average 12 to 25 µm (Fig. 3-11;
Table 3-6). A thick cell wall surrounds the round
to spherical cyst. As with the trophozoite, the
cyst nuclei are readily discernible. One to eight
nuclei with the typical nuclear features may be
seen in unstained as well as stained preparations.
Occasionally, large cysts containing 16 or more
nuclei may be present. The granular cytoplasm
of young cysts may contain a glycogen mass. On
occasion, the glycogen mass may displace the