Entamoeba coli

Disease / Pathogenesis

This amoeba is not considered to be a cause of disease.

The identification of this parasite is important in distinguishing it from Entamoeba histolytica which is a major cause of amebic dysentery and amoebiasis. It is also an indicator of the consumption of contaminated water which can be a source of another enteric pathogen not tested for.

Location in the Host

Lumen of colon and cecum

Geographic Distribution

Worldwide distribution.

Life Cycle

Transmission is through the ingestion of the cyst form of the ameba which will be in contaminated water or food.

Image courtesy of CDC

Morphology & Diagnosis

Entamoeba coli are detected in the feces during an ova & parasite examination. Trophozoite and cyst forms can be detected. As with all ameba the trophozoite and cyst forms are seen in liquid stool while cysts are generally only seen in formed stool.

The trophozoites range in size between 15-50u but normally are 20-24u in size. Unlike Entamoeba histolytica, the nucleus has a large karyosome that is not compact and more eccentrically located then centrally located. Coarse granules make up the peripheral chromatin unlike the fine granules that make up the peripheral chromatin of Entamoeba histolytica. Pseudopods when present are short and blunt.

The cyst form is 10-35u in size. Unlike Entamoeba histolytica, Entamoeba coli can have more than four nuclei present whereas the former has a maximum of four. The karyosome may appear compact or diffuse and be located centrally or eccentrically. The peripheral chromatin has coarse and irregularly clumped granules. A diffuse glycogen vacuole is sometimes present and chromatoid bars can be seen infrequently but when they appear they are splintered in appearance.


Entamoeba coli cyst in Trichrome stain – note the greater then four nuclei seen which help distinguish it from Entamoeba histolytica.
Photo by W. Vientos
Entamoeba coli trophozoite in a trichrome smear – photo by W. Vientos
Entamoeba coli cyst in trichrome stain – note the greater than 4 nuclei
Entamoeba coli cyst in formalin concentrate stained with Lugol’s Iodine – note the greater than 4 nuclei