Reaction of clinical isolates and typed strains of the family Bacteroidaceae with rabbit anti-Bacteroides sera examined by radial immunodiffusion.

Antisera were produced which were reactive with Bacteroides fragilis, B. gingivalis, or B. melaninogenicus subsp. melaninogenicus. Anti-B. gingivalis serum exhibited strong reactions with strains of homologous species and reacted with only one other species, B. thetaiotaomicron. Antigens shared by organisms of the B. fragilis group and B. melaninogenicus subspecies of the Bacteroidaceae must be considered when serological methods are used for their identification.