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Entamoeba gingivalis

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Causal Agents

Entamoeba gingivalis is a non-pathogenic ameba that inhabits the human oral cavity and occasionally other sites. Although it is often found in conjunction with periodontal disease, no causative association has been definitively identified.

Other human-infecting species of Entamoeba are discussed under Amebiasis and Intestinal Amebae.

Life Cycle

Life Cycle
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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. 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 trophozoite stage of E. gingivalis is morphologically similar to that of E. histolytica. The two should be differentiated, as both can be coughed up in sputum specimens (if E. histolytica is present in pulmonary abscesses).

Geographic Range

E. gingivalis is a cosmopolitan species and is very common globally.

Clinical Presentation

E. gingivalis is common in individuals with poor oral hygiene or periodontal disease. However, several studies have not definitely demonstrated any causative correlation. It appears that diseased periodontal tissue and associated Actinomyces bacteria simply provide a favorable environment for the ameba to develop. Occasionally, E. gingivalis trophozoites have also been reported from the female genital tract, particularly in association with use of an intrauterine device (IUD).

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 may also extend agranular pseudopodia while the main cell cytoplasm remains granular in appearance. Living specimens can move quickly.

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.
E. gingivalis trophozoites stained with Papanicolaou’s (Pap) stain.

 

Figure A
Figure A: Trophozoite of E. gingivalis (arrow) stained with Papanicolaou’s (Pap) stain.
Figure B
Figure B: Trophozoite of E. gingivalis, stained with Papanicolaou’s (Pap) stain.
Figure C
Figure C: Trophozoite of E. gingivalis, stained with Papanicolaou’s (Pap) stain. Note ingested host material such as epithelial cells and leukocytes (arrow).
Figure D
Figure D: Trophozoite of E. gingivalis, stained with Papanicolaou’s (Pap) stain. Note ingested host material (epithelial cells and leukocytes)
Figure E
Figure E: Trophozoite of E. gingivalis, stained with Papanicolaou’s (Pap) stain, showing an extended pseudopod (arrow).

Laboratory Diagnosis

Identification of E. gingivalis is usually made by the finding of trophozoites in scrapings of the gums and teeth; trophozoites may be seen ingesting white cells and epithelial cell nuclei. Two genetic sub types exist, the ST1 and ST2-kamaktli subtypes, though any clinical significance or morphologic differences between these two have not been investigated at the time of writing. E. gingivalis may be found in sputum on rare occasions or detected in cervical Pap smears. 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 and invading the female genital tract.

 

Laboratory Safety

Standard precautions apply for the processing of sputum samples.

Suggested Reading

Bradbury, R.S., Roy, S., Ali, I.K., Morrison, J.R., Waldner, D., Hebbeln, K., Aldous, W., Jepson, R., Delavan, H.R., Ndubuisi, M. and Bishop, H.S., 2019. Case Report: Cervicovaginal Co-Colonization with Entamoeba gingivalis and Entamoeba polecki in Association with an Intrauterine Device. The American Journal of Tropical Medicine and Hygiene, 100 (2), pp.311-313.

Garcia, G., Ramos, F., Maldonado, J., Fernandez, A., Yáñez, J., Hernandez, L. and Gaytán, P., 2018. Prevalence of two Entamoeba gingivalis ST1 and ST2-kamaktli subtypes in the human oral cavity under various conditions. Parasitology Research 117 (9), pp.2941-2948.

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