Light-microscopical appearance and ultrastructure of Blastocystis hominis, an intestinal parasite of man.

A study on Blastocystis hominis was undertaken for the purpose of clarifying the morphology of the organism using the following techniques; Giemsa, Heidenhain Iron Hematoxylin, and DAPI stains, phase-contrast microscopy, and transmission- and scanning-electron microscopy. Microscopic examinations of the lumen fluids aspirated at the endoscopical examination revealed the habitation of B. hominis in the lower ileum and cecum of a patient. When examined light-microscopically, organisms from stool materials, cultures, and aspirated intestinal lumen contents of a patient showed morphological resemblances to each other except for variations in size. Vacuolated cells, which were spherical in shape and characteristically had a large central vacuole and a narrow rim of cytoplasm containing nuclei and some inclusions, were the only form of the organism observed in this study, although the contents of the vacuole notably varied. DAPI stains clearly revealed the nucleus and the possible mitochondrion in the narrow rim of cytoplasm. Phase-contrast microscopy of fresh material prepared with physiological saline was recommended for diagnosis. When examined electron-microscopically, the organisms were coated with a capsule that was composed of fine filamentous materials. All the organisms contained a central vacuole although the contents of it varied considerably. The cytoplasm gave the organism a signet ring appearance and contained cristate mitochondria, a great number of ribosomes, Golgi's apparatuses, cytoplasmic microtubules, and nuclei with a nucleolus. Very few of the ultrastructures are those that would be expected of a yeast. Recent occurrences of B. hominis infection in Kyoto City, Japan, during a two-year period (June 1983 to August 1985) were also reported.