Entamoeba gingivalis
Entamoeba gingivalis is an Entamoeba histolytica-like amoebae that lives in/on the teeth, gums, and sometimes tonsils. It measures 10-35 micrometers in length. Endocytotic vacuoles are often numerous and the parasite will ingest bacteria, leukocytes, and erythrocytes (dark circles in trophozoites, above) although it is not itself invasive. No cysts are formed and transmission is entirely by oral-oral contact. Multiple samplings reveal the parasite to colonize the oral cavity of nearly all adult humans.
Here’s a fun fact. Several reports have documented colonization of the uterus by Entamoeba gingivalis. One intriguing study (1980, Acta Cytol. 24: 413-420) revealed about 10% of all intrauterine devices (IUDs) to be colonized by the filamentous plaque causing bacterium, Actinomyces. This bacterium is one favorite food item of Entamoeba gingivalis. Of those women with IUDs colonized by Actinomyces, approximately 10% of those also harbored the amoeba (IUDs without the bacterium had no amoebae). Thus, about 1% of all females with IUDs are thought to harbor uterine E. gingivalis. Food for thought?