[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/) › Commensal intestinal amoebae (Entamoeba coli, E. dispar, Endolimax nana and others) [Microbiology](https://durgical.com/en/microbiology/) · [Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/) # Commensal intestinal amoebae (Entamoeba coli, E. dispar, Endolimax nana and others) - Parasite - For completeness Amoebae that live in the gut without causing disease. They often appear on stool reports and signal contact with feces, not a need to treat. Updated 2026-11-01 Also called: non-pathogenic amoebae, Iodamoeba bütschlii, Entamoeba hartmanni ## Key points - E. coli: cyst with up to eight nuclei; commensal. - E. dispar is identical to E. histolytica under the microscope but is not pathogenic. - Iodamoeba: large glycogen vacuole that stains with iodine. - Finding commensals means fecal exposure, not disease; they are not treated. ## At a glance **Shape** Amoeboid trophozoite and cyst; the number of nuclei helps identify them **Family** Entamoebidae **Type** Non-invasive intestinal amoebae **Stain** Iodine and trichrome on stool exam **Size** E. coli: cyst about 10 to 35 µm; E. nana: about 5 to 10 µm ## Morphology - Entamoeba coli: cyst with up to eight nuclei (sometimes more); the only human Entamoeba with more than four. - Entamoeba hartmanni: like E. histolytica but smaller. - Entamoeba dispar: identical to E. histolytica under the microscope, but non-invasive. - Endolimax nana: small, cyst with four tiny nuclei. - Iodamoeba bütschlii: cyst with a large glycogen vacuole that stains brown with iodine. ## Transmission - Fecal-oral: swallowing cysts in contaminated water, food or hands. - The same routes as pathogenic amoebae, so they share risk factors. **Reservoir:** Humans (E. polecki also in pigs and primates) ### Isolation precautions What the care team adds to standard precautions. - Standard ## Life cycle - Mature cysts are swallowed with water or food. - Trophozoites are released and live in the colonic lumen without invading. - They multiply by binary fission and feed on bacteria. - They encyst and leave in feces, surviving days to weeks. ## Virulence factors - No invasive capacity: they colonize without damaging the mucosa. - Their importance is epidemiologic: they show fecal exposure. ## Diseases it causes - Intestinal colonization without disease; finding them does not explain symptoms and needs no treatment. ## Clinical picture - They cause no symptoms. - If the patient has diarrhea, another cause must be sought, including an accompanying pathogenic amoeba. ## Diagnosis - Stool exam: counting cyst nuclei and looking at chromatoid bodies, karyosome and vacuoles. - Telling E. dispar from E. histolytica requires a specific antigen test or PCR. - Reporting the species helps avoid unnecessary treatment. ## Treatment No treatment is needed. If they appear alongside symptoms, other causes are investigated before giving an antiparasitic. Drug class only; doses and regimens are set by the clinician from the current guideline. ## Prevention - Safe water and handwashing. - Basic sanitation: their presence in a community signals failures in excreta disposal. **Vaccine:** Not applicable. ## In Colombia They are very common findings in stool exams of Colombian children and adults. Prescribing antiparasitics for a report of E. coli, E. nana or unconfirmed «E. histolytica/E. dispar» is a common error worth avoiding. ## Memory aid «Eight nuclei, zero problems»: if the Entamoeba cyst has more than four nuclei, it is coli and can be left alone. ## Test yourself Think of the answer, then tap the question to see it. ## How many nuclei can an Entamoeba coli cyst have? Up to eight, sometimes more; it is the only human Entamoeba with more than four nuclei in the cyst. ## Which commensal amoeba cannot be told from E. histolytica under the microscope? Entamoeba dispar; a specific stool antigen test or PCR separates them. ## What is done about a stool report of Endolimax nana in a child without symptoms? No treatment: it is a commensal amoeba. Safe water and hygiene are reinforced, because it signals fecal exposure. ## Which feature identifies Iodamoeba bütschlii? Its cyst has a large glycogen vacuole that stains reddish-brown with iodine. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/commensal-intestinal-amoebae/) ## Related - [Entamoeba histolytica](https://durgical.com/en/microbiology/entamoeba-histolytica/) - [Blastocystis spp.](https://durgical.com/en/microbiology/blastocystis-spp/) ## What the colours mean **Gram-positive** Thick peptidoglycan wall: stains purple. **Gram-negative** Thin wall with an outer membrane: stains pink. **Acid-fast** Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain. [← Back to the group: Intestinal and urogenital protozoa](https://durgical.com/en/microbiology/groups/intestinal-and-urogenital-protozoa/) Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [CDC - DPDx - Intestinal (Non-Pathogenic) Amebae](https://www.cdc.gov/dpdx/intestinalamebae/index.html) (CDC, 2024); [CDC - DPDx - Amebiasis](https://www.cdc.gov/dpdx/amebiasis/index.html) (CDC, 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/microbiology/commensal-intestinal-amoebae/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/commensal-intestinal-amoebae/