Abstract
Lipopolysaccharide (LPS) extracted with phenol-water from four oral strains of Bacteroides melaninogenicus was found to be serologically active in precipitation and complement fixation tests and sensitized sheep erythrocytes to agglutination. Except for the capacity to inhibit indirect hemagglutination, the serological activity was destroyed by oxidation with periodate. The isolated LPS was antigenic in rabbits, giving rise to low- and high-molecular-weight antibodies. Cross-reactivity experiments revealed the presence in LPS of both type-specific and group-reactive antigenic determinants.