Serological diagnosis of Staphylococcus aureus septicaemia and endocarditis by means of crossed immuno-electrophoresis.

The diagnostic sensitivity and specificity were determined for serological diagnosis of Staphylococcus aureus endocarditis and septicaemia by means of crossed immuno-electrophoresis with intermediate gel. The antibody responses to S. aureus antigens in sera from 19 patients with S. aureus endocarditis and 51 patients with S. aureus septicaemia were compared with findings in 30 patients with non-S. aureus endocarditis and 30 patients with non-S. aureus septicaemia. Two of 55 S. aureus antigens, no. 18 (cross-react serologically with cell wall teichoic acid) and no. 46 of the reference pattern, were useful for serological diagnosis. The precipitin score, taking into account both the total number of precipitins and their titres, was the most useful diagnostic criterion. The present method can be used in selected cases to discriminate between S. aureus and non-S. aureus endocarditis. In cases with septicaemia only a positive test is of clinical value.