BACTEROIDES-FRAGILIS STRAINS EXPRESS MULTIPLE CAPSULAR POLYSACCHARIDES

Previous studies by our group have demonstrated that the capsule of Ba cteroides fragilis type strain NCTC 9343 consists of two chemically di stinct polysaccharides, designated PS A and PS B. These polysaccharide s can be isolated as an aggregate from the surface of the organism and give a complex multiprecipitin profile when they are reacted with hom ologous antiserum in an immunoelectrophoresis assay. Following structu ral analysis of PS A and PS B, we have determined that the complex pre cipitin profile is formed as a result of the differing electrophoretic and antigenic properties associated with each of these polymers. Pres ently, we have examined the capsular polysaccharides of 13 other strai ns of B. fragilis according to methods used for the prototype strain. The capsules of these strains were extracted, partially purified, and analyzed by immunoelectrophoresis at pH 7.3. Following reaction with h omologous polyclonal antisera, each of the capsular preparations teste d yielded a complex precipitin profile similar to that of the prototyp e strain. When reacted by immunoelectrophoresis with polyclonal antise rum to 9343 or with monoclonal antibodies to PS A and PS B, these caps ular preparations appeared to be antigenically diverse; some preparati ons (50%) showed complete or partial cross-reaction. These results sug gest that the dual polysaccharide motif seen with the prototype strain is a common feature of B. fragilis strains. In addition, the antigeni c heterogeneity of B. fragilis capsular polysaccharides could be used for the development of a serological typing scheme.