Study of Dientamoeba fragilis Jepps & Dobell I. Electronmicroscopic Observations of the Binucleate Stages II. Taxonomic Position and Revision of the Genus*

Abstract

SYNOPSIS. Light-and electronmicroscopic observations on Dientamoeba fTagilis strain A (Bi) 1 dealing primarily with the binucleate (arrested telophase ) stages, predominant in all populations, revealed the microtubular nature of the extranuclear spindle which extends between the 2 polar complexes each adjacent to one of the nuclei. The spindle microtubules originate in paired, nonperiodic structures apparentIy homologous to the "atractophores" described from hypermastigotes. To the external surface of the atractophores are applied periodic elements, which extend laterally as the parabasal filaments. Extensive Golgi complexes overlie the filaments, these structures corresponding to the components of the parabasal apparatus known from trichomonads and hypermastigotes. The 2-layered structures, consisting of the atractophores and periodic layers, together with the proximal parts of the Golgi complex and the spindle microtubules constitute the polar complex. No kinetosomeor centriole-like organelles have been found in the polar complexes or elsewhere in the organism. The extranuclear spindle is composed of 2 microtubule bundles, each with -30-40 mirrotubules. One of the bundles always appears at some distance from the nucleus; the other is juxtanuclear and is seen often to course within a groove of the nuclear envelope. A M e d . Hyg. 56, 535-7. 97. -1972. Structure and movement of Entamoeba. Ann. Trop. M e d . Parasit. 66, 329-34. 245-52. 77, 185-205.

Emerging from Obscurity: Biological, Clinical, and Diagnostic Aspects of Dientamoeba fragilis

“…In the latter set of samples only one genotype has been found. The rarer of the two genotypes was found in only two cases; one of these strains happens to be the isolate Bi/pa studied by Camp et al (13) and Silberman et al (115). This indicates that the results of studies using isolate Bi/pa may not be representative of the species as a whole.…”

“…Electron microscopy revealed electron-dense rounded inclusions in the cytoplasm that were termed "microbody-like" and were presumed to be homologous to the paraxostylar granules of trichomonads (13) (Fig. 3).…”

“…Phylogenetic analysis of the D. fragilis small-subunit rRNA gene sequence (115), using the same strain that had been studied at the morphological level by Camp et al (13) (strain Bi/pa; ATCC 30948), unequivocally confirmed its trichomonad affinities; more recently, analysis of the same gene from H. meleagridis confirmed the close and specific relationship between Histomonas and Dientamoeba (48). The latter investigation hinted at a link between Histomonas/Dientamoeba and the genus Tritrichomonas, but this remains to be confirmed.…”

“…Curiously, only a handful of papers have been published on the morphology of D. fragilis on the basis of transmission electron microscopy (13,91,112,113 (36). An extranuclear spindle is found between the nuclei, originating from polar complexes adjacent to one of the nuclei.…”

Molecular Testing for Clinical Diagnosis and Epidemiological Investigations of Intestinal Parasitic Infections

“…2C) was first described in 1918 as an amoeba of the intestinal tract of humans (109). Later, by means of antigen and ultrastructural studies and analysis of rRNA, however, the organism was reclassified as a trichomonad flagellate although lacking external flagella (110)(111)(112). Since its discovery, the pathogenicity of this organism has remained controversial.…”