Crossed immunoelectrophoresis and enzyme-linked immunosorbent assay of the cell-surface antigens of Bacteroides fragilis.

Antisera were raised to whole, live cells of a reference strain (NCTC 9344) and two clinical isolates (GNAB 92 and GNAB 4) of Bacteroides fragilis. Each antiserum was reacted in crossed line immunoelectrophoresis (CLIE) with EDTA-heat-sonication-prepared outer membrane (OM) complex from 10 B. fragilis strains. In addition, the antisera were reacted with these antigens in an enzyme-linked immunosorbent assay (ELISA). In CLIE, the antisera raised to the reference strain and one of the clinical isolates (GNAB 92) demonstrated a heat labile antigen which was common to all 10 of the test strains. Lipopolysaccharide (LPS) prepared from both the clinical isolates produced three major precipitin lines when reacted with their homologous antisera in crossed immunoelectrophoresis (CIE). In both cases, these three antigens were present as major components of the OM complex. Each antiserum reacted significantly in ELISA with all test OM complex preparations. Inhibition of ELISA showed that carbohydrates were the predominant cross-reactive antigens in ELISA and that in the case of the clinical isolate GNAB 4, most of the cross-reactive antigenic activity was present in the homologous LPS preparation.