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Intestinal Amebae

[Endolimax nana] [Entamoeba coli] [Entamoeba gingivalis] [Entamoeba hartmanni] [Entamoeba polecki] [Iodamoeba buetschlii]

Causal Agent

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic and reside in the large intestine of the human host. Entamoeba gingivalis is also considered nonpathogenic and resides in the oral cavity of the human host, in the gingival pockets at the base of the teeth.

Life Cycles

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic and reside in the large intestine of the human host The letter A. Both cysts and trophozoites of these species are passed in stool and considered diagnostic The number 1. Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool. Colonization of the nonpathogenic amebae occurs after ingestion of mature cysts in fecally-contaminated food, water, or fomites The number 2. Excystation occurs in the small intestine The number 3 and trophozoites are released, which migrate to the large intestine. The trophozoites multiply by binary fission and produce cysts, and both stages are passed in the feces The number 1. Because of the protection conferred by their cell walls, the cysts can survive days to weeks in the external environment and are responsible for transmission. Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment.

There is no known cyst stage for Entamoeba gingivalis; trophozoites live in the oral cavity of humans, residing in the gingival pockets near the base of the teeth The letter A. They are not considered pathogenic, and feed on bacteria and other debris. Trophozoites are transmitted person-to-person orally by kissing or fomites (such as eating utensils) The number 1. The trophozoite stage of E. gingivalis is morphologically similar to that of E. histolytica, and the two should be differentiated, as both can be coughed up in sputum specimens (for the latter, when present in pulmonary abscesses).

Geographic Distribution

All six species are distributed worldwide. Entamoeba polecki in nature is primarily a parasite of pigs and monkeys, and human infection is more prevalent in areas where the people have animal contact.

Clinical Presentation

Entamoeba coli, E. hartmanni, E. polecki, Endolimax nana, and Iodamoeba buetschlii are generally considered nonpathogenic, although they have been found in the stool of patients presenting with diarrhea where no known pathogens were identified. Their presence in stool can be an indicator of fecal contamination of a food or water source, and does not rule-out the presence of other parasites. Entamoeba gingivalis is also considered nonpathogenic, but is found in about 95% of patients with gum disease and about 50% of patients with healthy gums.

Endolimax nana

Endolimax nana cysts in concentrated wet mounts.

 

Cysts of Endolimax nana are spherical to ellipsoidal in shape and measure 5 to 10 µm. Mature cysts possess four nuclei with large, karyosomes and no peripheral chromatin. The nuclei are not visible in unstained wet mounts, but are visible in iodine-stained wet mounts and permanent slides stained with trichrome. The cytoplasm may contain diffuse glycogen, but lacks chromatoid bodies.
	Figure A

Figure A: Cyst of E. nana in a direct wet mount, viewed under differential interference contrast (DIC) microscopy.

	Figure B

Figure B: Cyst of E. nana in a direct wet mount stained with iodine.

E. nana cyst stained with trichrome.

 

Cysts of Endolimax nana are spherical to ellipsoidal in shape and measure 5 to 10 µm. Mature cysts possess four nuclei with large, karyosomes and no peripheral chromatin. The nuclei are not visible in unstained wet mounts, but are visible in iodine-stained wet mounts and permanent slides stained with trichrome. The cytoplasm may contain diffuse glycogen, but lacks chromatoid bodies.
	Figure A

Figure A: Cysts of E. nana stained with trichrome.

	Figure B

Figure B: Cyst of E. nana stained with trichrome.

	Figure C

Figure C: Cyst of E. nana stained with trichrome.

	Figure D

Figure D: Cyst of E. nana stained with trichrome.

E. nana trophozoites stained with trichrome.

 

Endolimax nana trophozoites measure 6 to 12 µm and possess a single nucleus with a characteristically large, irregularly shaped, blot-like karyosome. The nucleus has no peripheral chromatin. Their cytoplasm is granular and often highly vacuolated. Trophozoites of E. nana can be difficult to distinguish from those of Iodamoeba buetschlii.
	Figure A

Figure A: Trophozoite of E. nana stained with trichrome.

	Figure B

Figure B: Trophozoites of E. nana stained with trichrome.

	Figure C

Figure C: Trophozoite of E. nana stained with trichrome.

	Figure D

Figure D: Trophozoite of E. nana stained with trichrome. Image courtesy of the Kansas Department of Health and Environment.

	Figure E

Figure E: Trophozoite of E. nana stained with trichrome.

Entamoeba coli

E. coli cysts in concentrated wet mounts.

 

Cysts of Entamoeba coli are usually spherical, but may be elongated, and measure 10 to 35 µm.  Mature cysts typically have 8 nuclei but may have as many as 16 or more. Entamoeba coli is the only species in the genus encountered in humans with more than four nuclei in the cyst stage. The nuclei may be seen in unstained as well as stained specimens. Karyosomes may be compact or diffuse, and are usually eccentrically located. Peripheral chromatin is present and is often coarse and granular, and irregularly arranged along the nuclear membrane, but may be more uniform. The cytoplasm of mature cysts may contain diffuse glycogen. Chromatoid bodies are seen less frequently than in E. histolytica. When present, they are usually splinter like with pointed ends and thus different from the chromatoid bodies of E. histolytica, which have rounded ends.
	Figure A

Figure A: Cyst of E. coli in a unstained concentrated wet mount. Six nuclei are visible in this focal plane.

	Figure B

Figure B: Cyst of E. coli in a concentrated wet mount stained with iodine. Five nuclei are visible in this focal plane.

	Figure D

Figure D: Cyst of E. coli in a concentrated wet mount stained with iodine. Five nuclei are visible in this focal plane.

	Figure E

Figure E: Cyst of E. coli in a concentrated wet mount stained with iodine. Five nuclei are visible in this focal plane.

	Figure C

Figure C: Cyst of E. coli in a concentrated wet mount stained with iodine. Seven nuclei are visible in this focal plane.

E. coli cysts stained with trichrome.

 

Cysts of Entamoeba coli are usually spherical, but may be elongated, and measure 10 to 35 µm.  Mature cysts typically have 8 nuclei but may have as many as 16 or more.  Entamoeba coli is the only species in the genus encountered in humans with more than four nuclei in the cyst stage.  The nuclei may be seen in unstained as well as stained specimens.  Karyosomes may be compact or diffuse, and are usually eccentrically located.  Peripheral chromatin is present and is often coarse and granular, and irregularly arranged along the nuclear membrane, but may be more uniform.  The cytoplasm of mature cysts may contain diffuse glycogen.  Chromatoid bodies are seen less frequently than in E. histolytica.  When present, they are usually splinter like with pointed ends and thus different from the chromatoid bodies of E. histolytica, which have rounded ends.
	Figure A

Figure A: Immature cyst of E. coli, stained with trichrome. Notice the presence of only two nuclei, and a large glycogen vacuole.

	Figure B

Figure B: Mature cyst of E. coli, stained with trichrome. Five nuclei are visible in this focal plane.

	Figure C

Figure C: Mature cyst of E. coli, stained with trichrome. In this specimen, at least five nuclei are visible in the shown focal plane.

	Figure D

Figure D: Mature cyst of E. coli, stained with trichrome. In this specimen, at least five nuclei are visible in the shown focal plane.

	Figure E

Figure E: Mature cyst of E. coli, stained with trichrome. This figure and Figure F represent the same cyst shown in two different focal planes. Eight nuclei can be seen between the two focal planes. Also, above the cyst in this figure, a trophozoite of Endolimax nana can be seen.

	Figure F

Figure F: Mature cyst of E. coli, stained with trichrome. This figure and Figure E represent the same cyst shown in two different focal planes. Eight nuclei can be seen between the two focal planes.

E. coli trophozoites stained with trichrome.

 

Trophozoites of Entamoeba coli usually measure 15 to 50 µm. The trophozoites possess a single nucleus with a characteristically large, eccentric karyosome and coarse, irregular peripheral chromatin. The cytoplasm is usually coarsely granular and vacuolated (often described as "dirty" cytoplasm). Pseudopodia may be seen, and are often short and blunt; movement in living trophozoites is nondirectional.
	Figure A

Figure A: Trophozoite of E. coli stained with trichrome.

	Figure B

Figure B: Trophozoite of E. coli stained with trichrome.

	Figure C

Figure C: Trophozoites of E. coli stained with trichrome.

	Figure D

Figure D: Trophozoite of E. coli stained with trichrome.

Entamoeba hartmanni

E. hartmanni cyst in a wet mount.

 

Cysts of Entamoeba hartmanni are similar to those of E. histolytica but smaller, measuring 5-10 µm. Mature cysts contain four nuclei that possess a small, discrete centrally-located karyosome and evenly-distributed peripheral chromatin. Cysts may not be visible in unstained specimens. The cytoplasm in mature cysts may contain diffuse glycogen and rounded or elongated chromatoid bodies with rounded ends.
	Figure A

Figure A: Cyst of an E. hartmanni in a wet mount, stained with iodine.

E. hartmanni cysts stained with trichrome.

 

Cysts of Entamoeba hartmanni are similar to those of E. histolytica but smaller, measuring 5-10 µm. Mature cysts contain four nuclei that possess a small, discrete centrally-located karyosome and evenly-distributed peripheral chromatin. Cysts may not be visible in unstained specimens. The cytoplasm in mature cysts may contain diffuse glycogen and rounded or elongated chromatoid bodies with rounded ends.
	Figure A

Figure A: Cyst of E. hartmanni stained with trichrome. Notice the bluntly-ended chromatoid bodies.

	Figure B

Figure B: Cyst of E. hartmanni stained with trichrome.

E. hartmanni trophozoites stained with trichrome.

 

Trophozoites of Entamoeba hartmanni usually measure 5-15 µm. These trophozoites possess a single nucleus that contains a small, compact centrally or eccentrically-located karyosome and fine, uniform peripheral chromatin. Nuclei are usually not visible in unstained specimens. The cytoplasm is finely granular. Movement in living trophozoites is described as nonprogressive.
	Figure A

Figure A: Trophozoite of E. hartmanni stained with trichrome. Image courtesy of the Kansas Department of Health and Environment.

	Figure B

Figure B: Trophozoite of E. hartmanni stained with trichrome.

	Figure C

Figure C: Trophozoite of E. hartmanni stained with trichrome. In the upper-right of the image is a cyst-like body of Blastocystis hominis.

	Figure D

Figure D: Trophozoite of E. hartmanni stained with trichrome.

	Figure E

Figure E: Two trophozoites of E. hartmanni stained with trichrome.

	Figure F

Figure F: Trophozoite of E. hartmanni stained with trichrome.

Entamoeba polecki

E. polecki cyst in a concentrated wet mount, stained with iodine.

 

Cysts of Entamoeba polecki measure 9 to 25 µm and are usually uninucleate, but binucleate forms are seen rarely. The nucleus is often large, measuring up to one-third of the diameter of the cyst. The karyosome is pleomorphic, and may be minute to large and compact to diffuse, and centrally or eccentrically-located. Peripheral chromatin may be light to heavy but is usually evenly distributed. Cysts also contain an inclusion mass of variable size and numerous chromatoid bodies, which may be small and round to large rods with round or splintered ends.
	Figure A

Figure A: Cyst of E. polecki in a wet mount, stained with iodine. Notice the numerous chromatoid bodies (arrows).

E. polecki cysts stained with trichrome.

 

Cysts of Entamoeba polecki measure 9 to 25 µm and are usually uninucleate, but binucleate forms are seen rarely. The nucleus is often large, measuring up to one-third of the diameter of the cyst. The karyosome is pleomorphic, and may be minute to large and compact to diffuse, and centrally or eccentrically-located. Peripheral chromatin may be light to heavy but is usually evenly distributed. Cysts also contain an inclusion mass of variable size and numerous chromatoid bodies, which may be small and round to large rods with round or splintered ends.
	Figure A

Figure A: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

	Figure B

Figure B: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

	Figure C

Figure C: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

	Figure D

Figure D: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

	Figure E

Figure E: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

	Figure F

Figure F: Cyst of E. polecki stained with trichrome. Notice the large nucleus with a pleomorphic karyosome and numerous variably-shaped chromatoid bodies.

E. polecki trophozoites stained with trichrome.

 

Trophozoites of Entamoeba polecki are often rounded, measuring 10 to 25 µm. The single nucleus is often distorted and irregularly-shaped, with a small to minute centrally-located karyosome. Peripheral chromatin is usually delicate and uniform. The cytoplasm is often vacuolated with a hyaline border. Blunt pseudopodia may be seen.
	Figure A

Figure A: Trophozoite of E. polecki stained with trichrome.

	Figure B

Figure B: Trophozoite of E. polecki stained with trichrome.

	Figure C

Figure C: Trophozoite of E. polecki stained with trichrome.

	Figure D

Figure D: Trophozoite of E. polecki stained with trichrome.

	Figure E

Figure E: Trophozoite of E. polecki stained with trichrome.

Iodamoeba buetschlii

Iodamoeba buetschlii cysts in concentrated wet mounts.

 

Cysts of Iodamoeba buetschlii vary from being nearly spherical to ellipsoidal, and measure 5-20 µm. Cysts contain a single nucleus that is not visible in either unstained or iodine-stained wet mounts. With permanent stains (such as trichrome), the nucleus contains a large, usually eccentric karyosome. Achromatic granules may or may not be present around the karyosome. An important diagnostic feature for this species is the presence of a large compact mass (vacuole) of glycogen in the cyst stage. Although this mass can be visible in unstained wet mounts, in iodine-stained preparations it takes on a darker, reddish-brown color. The glycogen vacuole does not stain with trichrome, but will still be visible as a well-defined mass.
	Figure A

Figure A: Cyst of I. buetschlii in an unstained concentrated wet mount. In these cysts, the glycogen vacuole can be seen as a large, oval refractile body.

	Figure B

Figure B: Cyst of I. buetschlii in an unstained concentrated wet mount. In these cysts, the glycogen vacuole can be seen as a large, oval refractile body.

	Figure C

Figure C: Cyst of I. buetschlii from the same specimen as seen in Figures A and B, but stained with iodine. In this cyst, the glycogen vacuole is more-easily observed as a dark-staining mass in the cyst.

	Figure D

Figure D: Cyst of I. buetschlii from the same specimen as seen in Figures A and B, but stained with iodine. In this cyst, the glycogen vacuole is more-easily observed as a dark-staining mass in the cyst.

I. buetschlii cysts stained with trichrome.

 

Cysts of Iodamoeba buetschlii vary from being nearly spherical to ellipsoidal, and measure 5-20 µm. Cysts contain a single nucleus that is not visible in either unstained or iodine-stained wet mounts. With permanent stains (such as trichrome), the nucleus contains a large, usually eccentric karyosome. Achromatic granules may or may not be present around the karyosome. An important diagnostic feature for this species is the presence of a large compact mass (vacuole) of glycogen in the cyst stage. Although this mass can be visible in unstained wet mounts, in iodine-stained preparations it takes on a darker, reddish-brown color. The glycogen vacuole does not stain with trichrome, but will still be visible as a well-defined mass.
	Figure A

Figure A: Cyst of I. buetschlii stained with trichrome. In this specimen, both the nucleus and large glycogen vacuole are visible.

	Figure B

Figure B: Cyst of I. buetschlii stained with trichrome. In this specimen, both the nucleus and large glycogen vacuole are visible.

	Figure C

Figure C: Cyst of I. buetschlii stained with trichrome. In this specimen, both the nucleus and large glycogen vacuole are visible (arrow).

	Figure D

Figure D: Cyst of I. buetschlii stained with trichrome. In this specimen, both the nucleus and large glycogen vacuole are visible.

I. buetschlii trophozoite stained with trichrome.

 

Trophozoites of Iodamoeba buetschlii measure 8 to 20 µm and possess a single nucleus with a large, usually central karyosome surrounded by refractile, achromatic granules. The cytoplasm is coarsely granular, vacuolated and can contain bacteria, yeasts or other materials. Movement in living trophozoites is sluggish and described as nonprogressive. The trophozoites of I. buetschlii can be difficult to distinguish from the trophozoites of Endolimax nana.
	Figure A

Figure A: Trophozoite of I. buetschlii stained with trichrome.

	Figure B

Figure B: Trophozoite of I. buetschlii stained with trichrome.

Entamoeba gingivalis

E. gingivalis trophozoites stained with trichrome.

 

There is no known cyst stage for Entamoeba gingivalis; trophozoites measure 10-20 µm.  Trophozoites possess a single nucleus that contains a small, centrally-located karyosome and fine peripheral chromatin. The cytoplasm often contains ingested leukocytes, bacteria and other debris, very rarely red blood cells. The trophozoites also possess pseudopodia; living specimens can move quickly. Entamoeba gingivalis normally lives in the gingival pockets near the base of the teeth in the human mouth, and may be coughed up in sputum specimens. As such, it is important to differentiate this species from E. histolytica, which may be found in sputum from pulmonary abscesses.
	Figure A

Figure A: Trophozoite of E. gingivalis from culture, stained with trichrome.

	Figure B

Figure B: Trophozoite of E. gingivalis from culture, stained with trichrome.

	Figure C

Figure C: Trophozoite of E. gingivalis from culture, stained with trichrome.

	Figure D

Figure D: Trophozoite of E. gingivalis from culture, stained with trichrome.

Diagnostic Findings

For E. coli, E. hartmanni, E. polecki, E. nana, and I. buetschlii, identification is made by observing cysts and/or trophozoites in stool specimens, both concentrated wet mounts and permanent stained smears. Identification of E. gingivalis is made by the finding of trophozoites in scrapings of the gums and teeth. They may also be found in sputum in rare occasions. As such, it is important to differentiate them from the morphologically-similar trophozoites of E. histolytica, which may be found in sputum from pulmonary abscesses.

More on: Morphologic comparison with other intestinal parasites

Treatment Information

As these six species are generally considered nonpathogenic, there are currently no treatment recommendations for them.

DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: May 3, 2016
  • Page last updated: May 3, 2016
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