Immunochemical and biological studies of antigens isolated from a strain of Bacteroides fragilis

The cell-surface antigens of Bacteroides thetaiotaomicron

Three strains of B. thetaiotaomicron of different origin were investigated. Lipopolysaccharides were extracted from the studied strains using a phenol-water method. The best purification of LPS was achieved by digestion with nuclease and subsequent ultracentrifugation. Capsular material (CPS) was obtained from the most heavily encapsulated strain. The preparation were analyzed chemically, and their serological activity was determined. All antigens were active with homologous antibacterial sera in immunodiffusion, crossed immunoelectrophoresis, and passive hemagglutination tests. In the CPS equal amounts of saccharides and proteins were detected. All antigens were analyzed by polyacrylamide gel electrophoresis with SDS. Capsular antigen slowly migrated in the gel in the form of a single band. Migration pattern of lipopolysaccharides of the studied B. thetaiotaomicron strain was characteristic for S-type LPS.

Immunochemical investigations of antigens isolated from Bacteroides ovatus strain ATCC 8483

A saline extract (SE) and a phenol/water extract (WL) were prepared from Bacteroides ovatus strain ATCC 8483. A fraction CS was isolated from the culture supernatant. WL was further split by ultracentrifugation into lipopolysaccharide (LPS) and supernatant (L1). Fractions SE, WL, LPS and L1 reacted serologically with homologous antiserum but did not cross-react with antisera against heterologous Bacteroides serotypes. Fraction CS was inactive in haemagglutination, haemagglutination inhibition and immunoelectrophoresis tests. SE, WL, LPS and L1 proved to be serologically heterogeneous. A distinct serological specificity for SE was demonstrated. The serological reactivity in SE and WL was not altered after treatment with proteolytic enzymes yet completely destroyed in WL and partially in SE by sodium metaperiodate. SE, WL, LPS and L1 contained the sugar components rhamnose, fucose, ribose, mannose, galactose, glucose and glucosamine in different molar ratios for each fraction. Galactosamine was found in WL and LPS, uronic acid in WL and L1. Two unidentified aminohexoses were detected in WL, one of which was also detectable in L1 and SE. 2-Keto-3-deoxyaldonic acid was demonstrated in LPS and L1 after strong acid hydrolysis.