Localization of carbohydrate and DNA in cyst-like structures from a human intestinal spirochaete

This study examined the cyst-like structures found in human intestinal spirochaetes by transmission electron microscopy and by histochemical and immunocytochemical analysis. A human intestinal spirochaete which morphologically resembled other intestinal spirochaetes was grown anaerobically on blood agar plates and in Tryptone Soya broth (Oxoid) and harvested by centrifugation after 8 days growth. Specimens were either conventionally fixed for transmission electron microscopy or fixed in 0.5% glutaraldehyde in 0.1M sodium cacodylate buffer and embedded in LR White resin for immunocytochemistry. En bloc histochemical investigation using a periodic acid-thiosemicarbazide-silver proteinate technique was undertaken for the localization of carbohydrate. A post-embedding immunogold labelling technique was used on ultrathin sections to label DNA. Results from the histochemical study demonstrated a reaction product which was confined to the cytoplasm of mature spirochaetes and in the central bodies within the cysts. Immunogold labelling demonstrated the presence of DNA in both the mature protoplasmic cylinders and in the central bodies. The results of the present study indicate that spirochaetal cysts are highly organized structures, which contain both DNA and carbohydrate. These findings are compatible with the view that these structures have a functional role rather than representing degenerative artifacts.