Family Amoebidae

Members of this family are free-living or coprophilic. They have no flagellate phase. This family contains, besides Amoeba and a number of other free-living genera, several coprophilic species and one which can produce disease with a little human help.

Genus Acanthamoeba

These are relatively small amoebae without well developed ectoplasm. The nucleus is vesicular, with a large endosome. During mitosis, the nuclear membrane disappears at prophase. The mitotic figure at the end of metaphase is a straight or concave spindle with sharply pointed poles. The cysts are angular and polyhedric, with 2 membranes, the outer one being highly wrinkled and mammillated.

Acanthamoeba hyalina (Dobell and O'Connor, 1921) Volkonsky, 1931 (syn., Hartmannella hyalina) is a common coprophilic form. It occurs in soil and fresh water and is easily cultivated from old human and animal feces. Its trophozoites are 9 to 17 u in diameter when rounded. It has a single contractile vacuole and a single vesicular nucleus with a central endosome and peripheral chromatin. The cysts are spherical, 10 to 15 u in diameter, with a thin, smooth inner wall and a thick, wrinkled, brownish outer wall.

Walker (1908) described an amoeba from the intestinal tract of the turkey in Massachusetts under the name Ameba gallopavonis which Chatton (1953) listed as Acanthamoeba gallopavonis Walker. It had angular cysts and may be synonymous with A. hyalina.

Acanthamoeba has occasionally been encountered as a contaminant of tissue cultures and, because of its pathogenicity on injection and the resistance of its cysts to virucidal agents, it is a potential hazard in vaccines prepared from viruses grown in tissue culture.

Jahnes, Fullmer, and Li (1957) and Culbertson, Smith and Minner (1958) isolated an Acanthamoeba sp. from tissue cultures of trypsinized monkey kidney cells. The latter first recognized the amoebae in the lesions of monkeys which had died following inoculation of tissue culture fluid thought to contain an unknown virus but later shown to contain only Acanthamoeba. Following intracerebral and intraspinal inoculation into cortison- ized monkeys, the amoebae caused extensive choriomeningitis, destructive encephalomyelitis and death in 4 to 7 days. Following intracerebral inoculation into mice, they caused destructive encephalitis and death in 3 to 4 days. Following intranasal instillation into mice, they produced ulcers in the nasal mucous membrane and invaded the adjacent base of the skull, involving the frontal lobes of the brain and causing death in about 4 days. Following intravenous inoculation into mice, they caused perivascular granulomatous lesions in the lungs. These were associated with severe pneumonia, extensive fibrinopurulent exudate containing polymorphonuclear leucocytes and monocytes, hemorrhage, and invasion of the pulmonary veins followed by the formation of thrombi containing the amoebae.

McCowen and Galloway (1959) also isolated Acanthamoeba sp. from tissue cultures of trypsinized monkey kidney cells. They studied the pathogenicity for mice of this strain and of others isolated from the same source. The average sur-vival time of intracerebrally inoculated mice was approximately 5 days. Cysts remained virulent for mice after storage at -67°C for 15 months.

Genus Sappinia

In this genus the trophozoites have 2 closely associated nuclei with large endosomes. The cysts are binucleate also.

Sappinia diploidea (Hartmann and Nagler, 1908) Alexeieff, 1912 is a common coprophilic amoeba in the feces of man and other animals. Its trophozoites are 10 to 60 u long, with a thick, smooth, hyaline pellicle; according to Noble (1958), the ectoplasm has fine lines sometimes resembling wrinkles in cellophane. Two nuclei are present, usually pressed tightly together. Each nucleus has a large endosome and frequently a crescentic mass of granules between the endosome and the nuclear membrane. The cytoplasm is usually filled with many food vacuoles. A contractile vacuole is present, formed by the enlargement and coalescence of smaller vacuoles. A single, clear, broad pseudopod is characteristic, altho occasionally many pseudopods may be present. Cytoplasmic granules and food vacuoles are concentrated between the pseudopod and the rest of the body. Movement is quite sluggish. The cytoplasmic granules usually move rapidly. The cysts are typically binucleate, 12 to 18 u or more in diameter, with thick, uniform walls. The cysts are formed from 2 individuals which come together and secrete a common cyst wall; their nuclei fuse so that each one has a single nucleus, their cytoplasm fuses, each nucleus gives off reduction bodies, and the 2 remaining nuclei come into contact to make the cyst binucleate.

Noble (1958) found that S. diploidea appeared in fecal samples from Wyoming elk and bison (but not from cattle, horses and sheep) after storage at 4° C for a few days to a few weeks. It failed to survive in soil or in soil mixed with boiled feces, nor could it be found in soil samples taken from areas where elk, sheep or horses were present.

S. diploidea is readily cultivated. Noble (1958), for example, cultivated it both at 4° C and at room temperature on the surface of agar plates containing 1.5% agar, 0.05% yeast extract and 0.05% peptone. The cultures held at room temperature became moldy after 6 weeks. Sappinia was present for 2 to 3 weeks in the cultures at 4° C.

Genus Vahlkampfia

These are small amoebae with a nucleus containing a large endosome and peripheral chromatin, with polar caps during nuclear division. The trophozoites have a single broad pseudopod and move like a slug. The cysts have a perforated wall. The nucleus of this genus closely resembles that of Naegleria, but the latter has both flagellate and amoeboid stages. A number of species have been described from fresh water, old feces, lower vertebrates and invertebrates, but the taxonomy, nomenclature and validity of some of them are not certain.

Vahlkampfia punctata (Dangeard, 1910) Chatton and Lalung-Bonnaire, 1912 has been found in human feces. Its cysts have punctate markings.

Vahlkampfia lobospinosa (Craig, 1912) Craig, 1913 is another coprophilic species. Becker and Talbott (1927) found it in the rumen of a cow in Iowa. Its trophozoites are 10 to 24 u long. Its cysts have 1 or 2 nuclei and are 7 to 11 u in diameter.

Noble (1958) found that Vahlkampfia sp. appeared in fecal samples from Wyoming elk, bison, cattle, horses, sheep, moose and marmots after storage at 4° C for a few days to a few weeks. The proto-zoa persisted for several months. They failed to survive in soil, nor were they present in soil samples taken from areas where elk, sheep or horses were present. The trophozoites were 20 to 40 u in diameter, with finely granular cytoplasm filled with food vacuoles and other particles. A contractile vacuole was present. The pseudopods were broad, usually sluggish but sometimes formed almost explosively; often there was only a single, large pseudopod. The nucleus was vesicular, with a large, central endosome occasionally appearing to be composed of several closely packed granules. Peripheral chromatin was rarely present, altho a ring of minute granules was often present just within the nuclear membrane. The cysts were 8 to 15 u in diameter and almost exclusively mononucleate. The nucleus was different from that of the trophozoite. Its central endosome was usually smaller than in the trophozoite and often composed of several granules, and the peripheral chromatin was distinct, arranged in irregular clumps and often forming a crescent. A large vacuole and irregular chromatoid bodies, many of which resembled those of Entamoeba histolytica, were present. Noble believed that many of the cysts found in animal and human feces and described as those of Entamoeba are actually of the Vahlkampfia type.

Noble (1958) cultured this species at both 4° C and room temperature on the surface of agar plates containing 1.5% agar, 0.05% yeast extract and 0.05% peptone. The cultures held at room temperature became moldy after 6 weeks and were discarded, but Vahlkampfia was present for 3 months without attention in those held at 4° C.