Immunochemistry of R lipopolysaccharides of Escherichia coli. Different core regions in the lipopolysaccharides of O group 8.

Abstract

1 Acapsular (K−) forms were isolated from E. coli strains A295b (serotype 08:K42(A):H−) and E56b (serotype O8:K27(A):H−). A number of R strains were obtained from them by selection of spontaneous mutants, phage selection and mating experiments. 2 The (his−) R mutants were crossed with a (his+) Hfr S strain (O8) and selected for his+. Over 95% of the his+ recombinants were S forms. This showed that the R forms have a genetic defect which is closely linked to his. They all have a complete core structure in their lipopolysaccharides. 3 When the R strains were tested as to their sensitivity towards a number of phages it appeared that they can be divided into two groups. The discrimination was based on the sensitivity of the R mutants towards phages Br2, FO and C21. 4 Serological investigations of the corresponding lipopolysaccharides (using passive haemagglutination and its inhibition) indicated that the lipopolysaccharides obtained from the R mutants of E. coli O8:K42− were distinct from those obtained from the R mutants of E. coli O8:K27−. Thus two groups of R structures are present in E. coli O8:coli R1 (derived from O8:K27−) and coli R2 (derived from O8:K42−). The lipopolysaccharides belonging to coli R2 cross react with that of S. minnesota R60 (RII type). 5 The lipopolysaccharides of types coli R1 and coli R2 were subjected to mild acid degradation and the polysaccharide moieties were fractionated by gel chromatography. The results of chemical analysis were the following: coli R1 and coli R2 represent chemically distinct group of E. coli R lipopolysaccharides. Coli R1 lipopolysaccharides contain galactose, glucose and heptose in the molar ratios of 2:3:3 and coli R2 lipopolysaccharides contain galactose, glucose, glucosamine and heptose in the molar ratios of 2:4:1:4. Both types of lipopolysaccharides contain 1–1.5 moles of2-keto-3-deoxyoctonate per mole of galactose. After acid degradation and column fractionation the bulk of the polysaccharide moiety was obtained as core fraction. The molar rations of the constituents in these core fractions, with the exception of 2-keto-3-deoxyoctonate, were the same as in the corresponding degraded polysaccharides. It appeared that during degradation 1–2 2-keto-3-deoxyoctonate units (on a molar basis) were liberated. 6 Degradation and fractionation of S lipopolysaccharides (O8) yielded the core fraction and a high molecular weight fraction (mol. wt. about 10000). The latter consisted almost exclusively of mannose and had serological O8 specificity. The core fractions had the same composition as those obtained from the corresponding R mutants. Thus the lipopolysaccarides of E. coli O8 seem to consist of an identical O specific polysaccharide linked to individual core structures. These results show that there is more than one core type in lipopolysaccarides from different E. coli strains. Until now only one core type has been found in Salmonella and a different one in Shigella. Thus the findings reported here are not only of biochemical but possibly also of taxonomic interest.