A Freeze‐Fracture Electron Microscope Study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)1

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Abstract
Two strains of Trichomonas vaginalis, JH162A, with low pathogenicity, and Balt 44, with high pathogenicity, as well as 1 highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture EM. The protoplasmic faces (PF) of the cell membranes of all 3 strains of both species had similar numbers of intramembranous particles (IMP); the particles in the external faces (EF) of these membranes were least abundant in T. vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In T. foetus strain KV-1 the number of IMP in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad. In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of .apprx. 9 to 12 IMP on both the PF and EF. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture EM provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae, as represented by T. vaginalis, and of Tritrichomonadinae (the T. augusta-type), as exemplified by T. foetus, than was gained from previous transmission and scanning electron microscope studies. Typically 3 longitudinal rows of IMP on the PF of the recurrent flagellum of T. vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the 2 trichomonad species by the freeze-fracture method are discussed.