Structure and serology of the lipopolysaccharides: Cell components of citrobacter

The genus Citrobacter consists of enteric rods that utilize citrate as a sole carbon source. Citrobacter serotypes are normal intestinal inhabitants, but some of them have been reported in gastroenteritis and in extraintestinal infections. Our immumochemical studies on Citrobacter lipopolysaccharides of chemotype G comprised serotypes: 04, 027 and 036. As we found the serotypes mentioned above are distinguished in having O-specific polysaccharides that are homopolymers of β 1–2] linked 4-deoxy-D-arabinohexopyranose. In accordance with the structural indentity, the Citrobacter lipopolysaccharides showed strong serological cross-reactivity. Nevertheless, serotypes 04, 027, and 036 form separate entities, as observed in early studies of serologists. To find the reason for the immunological diversity the structural studies on lipopolysaccharide core regions of these Citrobacter serotypes were carried out. Three novel enterobacterial cores were identified. The complete cores 04 and 036 are decasaccharides differing in one structural element only: side-chain glucose is present in 04 oligosaccharide in the place of galactose in the 036. The core 027 is octasaccharide. In conclusion, our structural studies have shown hitherto that in Citrobacter chemotype G group only one O-specific polysaccharide, but three core regions, exist.