Light and electron microscopic localization of lipids in Blastocystis hominis.

Localization of the lipid of Blastocystis hominis was histochemically demonstrated. B. hominis was fixed with glutaraldehyde, treated with detergents, and stained with Sudan black B or Nile blue. The central vacuole of B. hominis stained with Sudan black B showed many black droplets with great variation in staining intensity. In Nile blue staining, the central vacuole showed many pinkish granules or homogeneous blue reactions. These results indicated the presence of neutral lipids and/or acidic lipids in the central vacuole. At the ultrastructural level, the central vacuole and some cytoplasmic vesicles showed enhanced electron density after post-fixation with imidazole-buffered osmium tetroxide solution. Great variation in the density and distribution of the electron-dense materials was observed in the central vacuole. Since the electron-dense vesicles were frequently observed in the cytoplasm, B. hominis may accumulate the lipid in the central vacuole, the function of which is not well known.