The O8 Antigen of Escherichia coli

Abstract

The polysaccharide moiety of the lipopolysaccharide (polysaccharide I) from Escherichia coli F492 (O8:K27−:H−) and the polysaccharide (polysaccharide II) from the rfa mutant F612 (derived from F492) were isolated by extraction with 45% aqueous phenol at 65°C. Polysaccharide I was obtained in 1–2% yield (based on dry bacteria). It contained mannose (83.5%), glucose (5.7%), galactose (3.4%), heptose (4.6%) and 2‐keto‐3‐deoxy‐mannosulonic acid (0.85%). Polysaccharide II was obtained in 0.8—1% yield (based on dry bacteria). It contained 99.2% mannose.With the method of Yphantis it was found that the molecular weights of polysaccharides I and II were 12400 and 10400, respectively. The difference accounted for the core oligosaccharide which was present in polysaccharide I and absent in polysaccharide II. The specific optical rotation was 43°C for polysaccharide I and 42°C for polysaccharide II.Both polysaccharides were permethylated. Subsequent hydrolysis, reduction and acetylation, followed by gas‐liquid chromatography and mass spectrometry indicated that in both polysaccharides two‐thirds of the mannose units were substituted at C‐2 and one‐third at C‐3. These results were confirmed by periodate oxidation.From polysaccharide II nine oligosaccharides were obtained after partial acid hydrolysis by chromatography on Biogel P2, paper chromatography and paper electrophoresis of the borate complexes. The oligosaccharides were reduced with sodium borodeuterate (which labelled the reducing mannose units) and methylated. After hydrolysis, reduction and acetylation the products were analyzed by gas chromatography and mass spectrometry.It is concluded that the polysaccharides I and II contain about 20 repeating units of α‐mannosyl‐1,2‐α‐mannosyl‐1,2‐α‐mannose which are joined through α‐1,3 linkages.