Role of immunoblotting in the diagnosis of culture negative and enterococcal endocarditis.

Serum samples from patients with endocarditis and septicaemia due to Enterococcus faecalis, Enterococcus faecium, Streptococcus bovis, and Streptococcus sanguis were immunoblotted against antigenic extracts from all four species. In E faecalis endocarditis there was a strong IgM response to E faecalis antigenic bands of 112, 88-90, and 45-47 Kd and a strong IgG response to 88-90 and 45-47 Kd bands. In E faecium endocarditis there was a pronounced IgG response to an E faecium band of 82-90 Kd. For S bovis endocarditis, there was a strong IgG response to several components of S bovis including bands of 66, 58, 52 and 4 Kd. For S sanguis, there was a strong IgG response to bands of 80-82, 76, 60 and 45 Kd. These patterns of antibody production were absent in patients with uncomplicated septicaemia and in controls. The delineation of these patterns enabled confirmation of the final diagnosis in seven patients initially suspected of having culture negative endocarditis.