Synonyms: Amoeba coli, Endamoeba hominis, Councilmania lafleuri.
This is the commonest species of amoeba in man. According to Beiding (1952), it was found in 28% in 19 surveys of 17,733 persons thruout the world and occurs in about 30% of the population of the United States. It also occurs in the gorilla, orangutan, chimpanzee, gibbon and in various species of macaques and other monkeys (Mackinnon and Dibb, 1938). Smith (1910) saw an amoeba similar to E. coli in pigs, and Kessel (1928a) found it in a Chinese pig. Kessel (1928a) also infected pigs experimentally with E. coli cysts from man, but the infections lasted less than 6 weeks.
Entamoeba coli occurs in the cecum and colon. It can be cultivated on the usual media. It is non-pathogenic, and therefore must be differentiated from E. histolytica.
Its trophozoites are 15 to 50 u (usually 20 to 30 u) in diameter. The cytoplasm is filled with bacteria and debris, and the ectoplasm is thin. The organism moves sluggishly. The nucleus has an eccentric endosome larger than that of E. histolytica, and a row of relatively coarse chromatin granules around its periphery. There may also be a few scattered chromatin granules between the endosome and the nuclear membrane. The cysts are 10 to 33 u in diameter and have 8 nuclei when mature. The cysts contain slender, splinter-like chromatoid bodies with sharp, fractured or square ends; these disappear as the cysts age. The young cysts also may contain a large, well-defined glycogen globule; it usually disappears before the cvst is mature.
Wenyon (1926) reported that he had seen 8-nucleate amoeba cysts of the E. coli type in the feces of goats. Galli-Valerio (1935) described this form, naming it Entamoeba wenyoni. The few trophozoites which he saw measured 12 by 9 u, their protoplasm was fairly granular with no distinction between ectoplasm and endoplasm, and they contained numerous bacteria. They moved very slowly with short, rounded pseudopods. The cysts were spherical, 6 to 9 u in diameter, and contained 8 nuclei.