Cytochemical electron microscopy on polysaccharide granules in the endogenous forms of Eimeria brunetti

The endogenous stages in the life cycle of Eimeria brunetti were tested for polysaccharide material by electron microscopical cytochemistry using the periodic acid-thiocarbohydrazide-osmium tetroxide (PATO)-method. The parasites were observed within the epithelial cells of the small intestine of infected domestic fowls. Two types of granules reacted positively for polysaccharide. The first was large, approximately 500 nm by 250 nm. These granules had an appearance similar to the polysaccharide granules reported for other coccidian parasites. They were observed in mature merozoites, macrogamonts, and developing oocysts. The second type of granule was smaller (15-30 nm in diameter) and was only observed at the periphery of the residual cytoplasmic mass of mature microgamonts. It was more similar in appearance to metazoan glycogen than the former. However, since the PATO-method does not differentiate between different polysaccharides it can not be proven if these granules in fast contain glycogen. The WFBI of the macrogamete and the outer layer of the oocyst wall gave a slight positive reaction but after examination of the controls it appeared that this was not a specific reaction for polysaccharides.