Electron microscopy of surface structures of Blastocystis sp. from different hosts.

Samples of Blastocystis sp. obtained from humans, monkeys, pigs and chickens were examined by scanning electron microscopy and transmission electron microscopy to compare surface structures. The surface coat of Blastocystis sp. cells from each host species showed some morphological variations, but these were not sufficiently different to allow judgement to be made on speciation. The surface structure morphology appeared similar for samples of Blastocystis sp. from the same host species. The surface coat of the cultured human isolate of B. hominis was much thinner than that of cells from fresh human faecal material, and the cell surface appeared to be smoother and without the small projections seen in the fresh forms. Bacteria were frequently found in association with the surface coat of Blastocystis sp. from all fresh faecal material. Possible functions of the surface coat, especially in relation to protection against osmotic shock, are discussed.