Humoral reactions in human endocarditis due to Streptococcus bovis: evidence for a common S bovis antigen

Humoral reactions to native culture filtrates of Streptococcus bovis were studied in patients with endocarditis by means of two-dimensional crossed immunoelectrophoresis. Serum from patients with S bovis endocarditis produced eight different precipitin arcs. Lex antigen cross-reacted with sera from patients with viridans streptococcal endocarditis, and TA antigen cross-reacted with ribitol teichoic acid-positive sera from patients with Staphylococcus aureus bacteremia. One antigen, common (c), was immunoreactive with all 10 sera from S bovis-infected patients. Antibody to this antigen was not found in sera from 77 patients with gram-positive bacteremia or in 29 other control sera. Common (c) antigen was found in all strains of S bovis isolated from patients. Rabbits immunized with formalinized S bovis cells of human origin also produced antibody to common (c) antigen. Common (c) may be an important antigen of S bovis and may in fact define this organism serologically.