Electron microscopic study of lipopolysaccharide from an avian strain of Escherichia coli O18.

The fine structure of lipopolysaccharide (LPS), isolated from an avian strain of Escherichia coli O18, was examined by electron microscopy. In positively stained preparations, ribbonlike structures with frequent branching were observed as previously reported (4). Two densely stained parallel lines were occasionally seen associated with a ribbon. When negative staining was employed, the LPS appeared as a branching ribbon with one central and two lateral zones divided by two relatively dense parallel lines running the complete length of the ribbon. The lateral zones were probably due to the O-antigenic side chains of the LPS. This interpretation was supported by the fact that the electron microscopic structure of the LPS from two rough strains, E. coli K-12 Gal 23 and Salmonella tuphimurium TV119 RII, both lacking the O-specific side chains, did not possess the outer lateral zones.