Synonyms: Amoeba gingivalis, Amoeba buccalis, Entamoeba buccalis, Amoeba dentalis, Amoeba kartulisi, Entamoeba rnaxillaris, Entamoeba canibuccalis.
This species occurs commonly in the human mouth, where it lives between the teeth, in the gingival margins of the gums and in the tartar. It has occasionally been found in infected tonsils. E. gingivalis is present in perhaps 50% of all humans, but in up to 95% of those with pyorrhea. It was once thought to be the cause of pyorrhea, but is now known to be a harmless commensal which finds an ideal home in diseased gums.
Hinshaw (1920) transmitted E. gingivalis to 5 dogs with gingivitis. In one of them the infection was still present after 11 1/2 months, but in the others it died out within 4 months. Kofoid, Hinshaw and Johnstone (1929) established persistent infections in 5 of 11 dogs with E. gingivalis from cultures. They could not infect dogs with healthy mouths, but only those with gingivitis, pus pockets or loose gums.
Goodrich and Moseley (1916) found amoebae indistinguishable from E. gingivalis in pyorrheic ulcers in the mouths of 2 dogs and a cat in England. Noller (1922) found it in dogs in Germany. Simitch (1938) found a small amoeba in the saliva of 3 out of 165 dogs in Serbia and named it E. canibuccalis.
The trophozoites were 8 to 16 u long but became as long as 25 u in culture. Simitch infected 2 old dogs with cultured protozoa but failed to infect 3 young dogs, a young wolf and 2 humans. In view of the affection with which some dog and cat owners treat their pets, there is no reason to believe that the entamoebae in the mouths of these animals are a different species from that of man.
Kirby (1928) found E. gingivalis in the mouths of 2 chimpanzees with pyorrhea. Kofoid, Hinshaw and Johnstone (1929) found it in the mouths of Macaca mulatta and M. irus. Deschiens and Gourvil (1930) found it in the M. mulatta and Papio sphynx. Hegner and Chu (1930) found it in the mouths of 37 out of 44 wild M. philippinensis.
E. gingivalis has no cysts. The trophozoites are usually 10 to 20 u long, but may range from 5 to 35 u. The cytoplasm consists of a zone of clear ectoplasm and granular endoplasm containing food vacuoles. The amoebae usually feed on leucocytes, epithelial cells, sometimes on bacteria and rarely on red blood cells. There are usually a number of pseudopods. The nucleus is 2 to 4 u in diameter, with a moderately small endosome, a peripheral layer of chromatin granules and some delicate achromatic strands extending from the endosome to the nuclear membrane.
Reproduction is by binary fission. It was described in detail by Child (1926), Stabler (1940) and Noble (1947). Child said that 6 chromosomes are present, but Stabler and Noble found only 5.