Entamoeba coli
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p596-597
2025-09-23
167
General Characteristics
The life cycle of E. coli is identical to that of E. dispar. After digestion of infective cysts, the organisms excyst in the intestinal tract and produce trophozoites. Cyst formation occurs as the gut contents move through the intestinal tract; the excreted cysts are the infective form that is transmitted to humans and some animals.
E. coli trophozoites are somewhat larger than those of E. histolytica and E. dispar and range from 15 to 50 µm in diameter ( Figures 1 and 2). Motility is sluggish with broad, short pseudopods. In wet preparations, differentiating nonpathogenic E. coli from pathogenic E. histolytica is almost impossible. On the permanent stained smear viewed at a higher magnification, the cytoplasm is granular with vacuoles containing bacteria, yeasts, and other food materials. The nucleus has a large blotlike karyosome that may be eccentric rather than centrally located. The chromatin on the nuclear membrane tends to be clumped and irregular. Although rare, if RBCs are present in the intestinal tract, E. coli may ingest them rather than bacteria.
Fig1. to C, Trophozoites of Entamoeba histolytica (note ingested red blood cells). D, Trophozoite of E. histolytica/E. dispar. E, Early cyst of E. histolytica/E. dispar. F to H, Trophozoites of Entamoeba coli. I and J, Cysts of E. coli.
Fig2. Entamoeba coli trophozoite.
Early cysts often contain chromatoidal bars, which tend to be splinter shaped and irregular. Eventually, the nuclei divide until the mature cyst, containing eight nuclei, is formed. In rare cases, the number of nuclei reaches 16. The cysts measure 10 to 35 µm in diameter, and as they mature, the chromatoidal bars disappear. When the cyst of E. coli matures, it becomes more refractive to fixation; therefore, the cyst may be seen on the wet preparation but not on the permanent stained smear. Occasionally, on trichrome smears, the cysts appear distorted and somewhat pink (Figure 3).
Fig3. Entamoeba coli cyst (trichrome stain) (poor preservation; typical appearance of some E. coli cysts).
Epidemiology
Transmission occurs through the ingestion of mature cysts from contaminated food or water. The organism is readily acquired, and in some warmer climates or areas with primitive hygienic conditions, the colonization rate can be quite high.
Pathogenesis and Spectrum of Disease
E. coli are considered nonpathogenic and do not cause disease.
Laboratory Diagnosis
Unless the mature cyst with eight nuclei is seen, the morphologies of E. histolytica, E. dispar, E. moshkovskii, and E. coli are similar in the trophozoite and immature cyst stages. E. moshkovskii is typically a free-living amoeba isolated in river or stream sediment and rarely infects humans. Definitive identification relies on examination of permanent stained smears.
Therapy
Specific treatment is not recommended for the nonpathogen E. coli. Correct differentiation among the species is critical to good patient care. Because the amebae are acquired through fecal-oral contamination, pathogens and nonpathogens can be found in the same patient. If few E. histolytica/E. dispar organisms are present among many E. coli organisms, extended microscopic examination and/or the use of species-specific immunoassay testing may be required to make the correct identification.
Prevention
Prevention depends on adequate disposal of human excreta and improved personal hygiene, preventive measures that apply to most of the intestinal protozoa.
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