Immunochemical studies of lipopolysaccharide and partially degraded lipopolysaccharide from Bacteroides fragilis IPL E323.

A serologically heterogeneous lipopolysaccharide (LPS) was prepared from B. fragilis IPL E323 by phenol-water extraction and purification by ultracentrifugation. The LPS was split by hydrolysis with 1 per cent acetic acid into an acid-soluble polysaccharide and insoluble material. Gel filtration of the acid-soluble material on Bio-Gel P-60 gave a high-molecular-weight fraction eluted with the void volume (Vo), which was serologically heterogeneous, and low-molecular-weight materials eluted at 2.5 x Vo and 2.7 x Vo. Some material was also eluted at 2.9-3.0 x Vo. The oligosaccharides eluted at 2.5 x Vo and 2.7 x Vo showed an antibody-neutralizing capacity similar to that of the parent LPS. Galactose, glucose and rhamnose were the only sugars present in these fractions. The material eluted at 2.9-3.0 x Vo, which contained the same neutral sugars, but at another molar ratio, was serologically inactive. SImilar results were obtained when LPS from three other B. fragilis strains were treated in the same way.