Serodiagnosis of Streptococcus faecalis endocarditis by immunoblotting of surface protein antigens

We describe a method for the serodiagnosis of Streptococcus faecalis in infective endocarditis which could be of value in culture-negative cases. Serum-grown cells of S. faecalis produced three major characteristic protein antigens (73,000, 40,000, and 37,000 molecular weight) which were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized whole cells. After electrophoretic transfer to a nitrocellulose membrane, these antigens were visualized by probing with serum from patients with endocarditis caused by S. faecalis. Serum from patients with endocarditis caused by other organisms did not react with the S. faecalis-specific antigens. This procedure should facilitate positive early diagnosis of S. faecalis endocarditis or establish its absence in culture-negative cases.