Human and animal serotypes of Bacteroides gingivalis defined by crossed immunoelectrophoresis

The antigenic complexity of three strains of Bacteroides gingivalis and four strains resembling B. gingivalis isolated from animals was analyzed and compared by crossed immunoelectrophoresis. Thirteen antigens of the human biotype were present in all human strains and six antigens of the animal biotype were present in all animal strains, indicating a marked serological homogeneity within each biotype. Four antigens cross-reacting between the human B. gingivalis and the animal strains were identified. This antigenic relatedness defined the serological homogeneity of the two biotypes within the species and allowed recognition of four species-specific antigens. Two antigens specific to the human strains and two antigens specific to the animal strains were identified, indicating that serotype-specific antigens can distinguish each biotype. It is thus proposed that the oral, black-pigmented asaccharolytic Bacteroides strains of animal origin be classified as catalase-positive variants of B. gingivalis. It is also proposed that two serotypes be recognized within the species B. gingivalis. Serotype 1 includes the catalase-negative human biotype, and serotype 2 includes the catalase-positive animal biotype.