Use of specific antibody to demonstrate glycocalyx, K99 pili, and the spatial relationships of K99+ enterotoxigenic Escherichia coli in the ileum of colostrum-fed calves.

The attachment of enterotoxigenic Escherichia coli (ETEC) strain B44 (O9:K30:K99:F41:H-) to the ileal epithelium of newborn colostrum-fed calves was studied by electron microscopy. Stabilization of the bacterial glycocalyx (K30) and pili (K99) by fixation of tissue sections in specific antibody and staining with ruthenium red were used so that the bacterial surface structures could be clearly visualized and their spatial relationship to the intestinal brush border defined. When sections of ileum from infected calves were neither fixed in antibody nor stained with ruthenium red, the ETEC cells colonizing the small intestine were separated from each other and from the brush border by an electron-translucent halo; neither the glycocalyx nor the pili could be clearly resolved. When ruthenium red staining was used, the halo was partially filled by a net of electron-dense fibers composed of pili and condensed glycocalyx which extended to the brush border. Tissue sections reacted with anti-K30 antibody before staining with ruthenium red revealed microcolonies of ETEC surrounded by a discrete electron-dense glycocalyx 0.3 to 1.0 micrometers thick and in tight contact with the epithelial cell surface. When ileal tissue was treated with K99 antibody, the K99 pili were visible as discrete fibers extending from the bacterial cell surface through the glycocalyx. We discuss the role of these cell surface components in pathogenic adhesion and in the formation of protected microcolonies at the surface of the infected ileal epithelium.