The fine structure of Entamoeba histolytica processed by cryo-fixation and cryo-substitution

Recently, the use of cryo-fixation followed by freeze-substitution has been shown to produce a better ultrastructural preservation of cellular components due to the rapidity of the fixation procedure and the lack of distortion during dehydration. When these techniques are applied to study the fine structure of axenically cultured trophozoites of E. histolytica, an improved preservation of cytoplasmic and nuclear components was found. The surface coat of the parasite appears much thicker and uniform than in conventionally treated samples. Also, the ground substance of the cytoplasm is packed with fibrogranular material, which is usually extracted by chemical fixation. The extremely fast fixation procedure allows the visualization of fusion and/or fission processes of cytoplasmic vacuoles and vesicles. Nuclear microtubules and cytoplasmic microfilaments are clearly identified. Low-temperature techniques allow not only a better preservation of the cell structure of E. histolytica parasites, but will also facilitate considerably future immunoelectronmicroscopical studies.