Release of membrane vesicles containing endotoxic lipopolysaccharide in Escherichia coli O157 : H7 clinical isolates

Membrane vesicles released by E. coli O157:H7 strains were investigated by immune-electron microscopy using anti-O157 antibody. Anti-O157 antibody enh anced the negative-staining of vesicles and we found numerous small vesicle s clearly formed around bacterial cells, An immunogold-electron microscopic examination confirmed that lipopolysaccharide (LPS) including the O-side c hain is present on the surface of the vesicles. Sodium dodecyl sulfate poly acrylamide gel electrophoresis analysis of the purified vesicles showed tha t the vesicles contained LPS consisting of a lipid-A and an O polysaccharid e, In addition, the endotoxic activity of the vesicle was confirmed by a li mulus test. These results suggest that the vesicles may play an important r ole in the pathogenesis of Escherichia coli O157:H7.