MONOCLONAL-ANTIBODIES TO DETECT CAPSULAR DIVERSITY AMONG BACTEROIDES-FRAGILIS ISOLATES

The capsular polysaccharide complex (CPC) of Bacteroides fragilis is c omposed of two distinct polysaccharides, designated PS A and PS B, and is a major virulence factor of this microorganism, In order to invest igate the antigenic diversity of the CPCs of B. fragilis strains, we g enerated and characterized 10 monoclonal antibodies (MAbs) directed tg the CPCs of three reference strains, The specificities of the MAbs we re determined by enzyme-linked immunosorbent assay and dot-immunobindi ng assay, At least one MAb was specific for each PS A and PS B of the three strains, The MAbs were used to detect capsular antigens on the s urface of 231 B, fragilis isolates from different geographical areas b y a whole-cell dot-immunobinding assay, Over half of the strains, rega rdless of the country of origin, reacted with at least one MAb, Clinic al extraintestinal infection isolates were significantly more reactive than fecal isolates, suggesting an association between capsular compo sition and the propensity to cause clinical infections, The patterns o f reactivity of the isolates with the 10 MAbs were very different and sometimes extremely complex and indicated a sharing of epitopes among different capsular polysaccharides, The reactive strains could be grou ped according to 32 different patterns; some patterns were relatively common, while others were rarer and were shown by only one or two stra ins, These results show that B, fragilis capsular polysaccharides are antigenically extremely diverse, This complexity and the large number of nonreactive strains indicate that a typing system based on B, fragi lis capsular antigens will be difficult to establish.