The core structures of Sliigelku sonnei phase I, phase I1 and R-form lipopolysaccharides have been investigated using the following methods : methylation analysis, Smith and enzymic degradations, H-NMR spectroscopy and passive hemolysis inhibition. The complete structures of the cores occurring in Sh. sonnei, as well as the type of linkage between the core and 0-specific chain, are proposed.Shigellu .sonnei comprises a single serological specificity termed phase I. Smooth colonies of phase I spontaneously dissociate to rough forms known as phase 11. The lipopolysaccharide of phase I is of the R I core type [I] and contains 0-specific side chains. Phase 11 lipopolysaccharide, however, is incomplete: although still of the R1 core type it is devoid of the 0-specific part. R-form is a more defective mutant of Slz. sonnei than phase I1 since its lipopolysaccharide has the incomplete core region.As shown by structural studies of Kenne et al.[2], the 0-specific polysaccharide of phase I lipopolysaccharide is composed of disaccharide repeating units formed from two rare sugars. N-Acetyl-L-altrosaminuronic acid as an r-pyranosyl residue substituted at 0-4, and linked to a 2-acetamido-4-aniino-2,4,6-trideoxy-~-~-galactopyranosyI residue through 0-3, represents the phase I repeating unit.A tentative structure for the hexose region of the Sh. .sonnei core has been published by Kontrohr and Kocsis [3], but neither the structure of the heptose region nor the anomeric configurations were defined. The preliminary structural information on the Sh. sonnei core region was also presented in our previous paper [4]. Recently Jansson et al. [5] performed complementary studies on the structure of the hexose regions of several enterobacterial (Eschrrichiu coli and Sulmondu) cores. For the majority of known enterobacterial lipopolysaccharides however, there is still a lack of information about how the 0-specific polysaccharide is bound to the core.The aim of the present study has been to establish the complete structure of the Sh. .sonnei core, comparing the core oligosaccharides isolated from phase I, phase TI and R-form lipopolysaccharides. The core material derived from phase I has shown some heterogeneity and thus was separated into four fractions. One of these fractions, composed of a phase-I-specific disaccharide unit linked to the core oligosaccharide, has proved to be extremely useful for the identification of the ~.

Lipopolysaccharides with sialic acid as a component were isolated from six bacterial serovars of the family Enterobacteriaceae. SDS‐polyacrylamide gel electrophoresis, immunoblotting and passive haemagglutination demonstrated that epitopes are localized in the O‐specific polysaccharide of lipopolysaccharides. The strains were tested for a serological relationship; the only distinct cross‐reactivity recorded was between Escherichia coli serovars O24 and O56. The molecular mimicry phenomenon was found for Citrobacter freundii serovar O37 which shared epitopes with horse as well as human red blood cells.

In the article the composition and structure of the O-specific polysaccharide chains and core region of the O antigens isolated from over 20 H. alvei strains is overviewed. Moreover, the correlation between the structure and immunospecificity of the O antigens is presented and discussed.