Page 75 - parasitology for medical and clinical laboratoryprofessionals

Protozoal Microorganisms as Intestinal Parasites 55

in the human gastrointestinal tract. The term E. coli is
MICROSCOPIC DIAGNOSTIC sometimes confused with the bacterium Escherichia

FEATURE coli, a Gram negative rod that is normal flora in the
bowel of humans except for some pathogenic strains
that often cause serious illness when contracted.
General Fresh cysts of Entamoeba coli contain what are called
Classification Amoeba
chromatoid bodies or bars and when they are pres-
Organism Entamoeba ent they will have sharply pointed and splintered ap-
histolytica pearances. The cysts are almost perfectly round and
Specimen Required Stool specimen contain granular and unevenly distributed peripheral
Stage Trophozoites most chromatin. The morphology of the Entamoeba coli cyst
diagnostic stage includes a spherical (round) shape and a range in size
Size Trophozoite—15–25 3 from 10 to 35 μm but is usually observed in the 15- to
5–15 μm; Cysts— 25-μm range. Chromatoid bodies are seen less often in
10–20 μm E. coli than in E. histolytica. When observed, they are
Shape Elongated usually splinter-like with pointed ends and differ from
trophozo-ites and the chromatoid bodies of E. histolytica, which have
round cysts rounded ends.
Motility Directional and Entamoeba coli is one of the larger cysts in intes-
progressive by tinal amoebae, containing eight nuclei, but careful fo-
pseudopodia cusing at different levels with a light microscope may
Nucleus(i) 1 for trophozoites be necessary to visualize all eight nuclei. Mature E. coli
and up to 4 for cysts usually have 8 nuclei (but it has been reported that
cysts sometimes 16 nuclei are present) in completely mature
Cytoplasm Clear and without cysts that measure 10 to 35 μm. In addition to at least 8
ingested particles nuclei, the mature cysts will have a large karyosome (cen-
or vacuoles
tral or eccentric) in each nucleus and an irregular (but
Other Features Tissue invasive; sometimes regular) chromatin pattern (Figure 3-13).
concentric bull’s Immature cysts contain 8 or fewer nuclei and may have
eye karyosome
in Chromatoidal one or two large nuclei with a large and easily discern-
bars with rounded able glycogen vacuole. The nuclei can be enumerated
terminal ends by carefully focusing up and down with the microscope
nucleus (nuclei)

Source: Centers for Disease Control and Prevention (CDC)
E. histolytica
Trophozoite Cyst

Delmar/Cengage Learning

FIGURE 3-13 Entamoeba coli cysts typically have
8 nuclei