Immunochemical differences between oral and nonoral strains of Bacteroides asaccharolyticus

We undertook a morphological and immunochemical comparison of purified outer membrane antigens from oral and nonoral isolates of Bacteroides asaccharolyticus. Electron micrographs of thin sections of whole bacteria revealed a compact, electron-dense capsule external to the outer membrane of oral strains. A loose, web-like material was noted on the surface of several nonoral strains that was distinct from the dense capsule seen on oral strains. Polyacrylamide gel electrophoresis showed distinct differences in the protein band pattern between oral and nonoral isolates; sugar composition was similar with a few exceptions. An indirect fluorescent-antibody test utilizing antiserum to a purified capsular antigen from a single oral strain cross-reacted with all of numerous oral and nonoral strains of B. asaccharolyticus, thereby demonstrating a shared antigen that is species specific for B. asaccharolyticus. However, antibodies to an oral strain-derived capsular antigen were detectable by enzyme immunoassay only in serum from rabbits immunized with oral strains. Thus, definite morphological and immunochemical differences were found between oral and nonoral isolates of B.asaccharolyticus.