Antiserum agar method for identification of Smith type exopolysaccharides in clinical isolates of Staphylococcus aureus.

We used an antiserum agar method to identify clinical Staphylococcus aureus strains producing an exopolysaccharide antigenically identical to the S. aureus Smith diffuse strain. S. aureus blood isolates were obtained from 137 patients, and three additional isolates were obtained from bone debridement. The 140 patients were clinically divided into the following groups: endocarditis (7 patients); pneumonia, empyema, or both (33 patients); intravascular device (34 patients); superficial or wound infection or both (35 patients); deep tissue infections (18 patients); and 6, unknown bacteremias (13 patients). Ninety (64.3%) of the total 140 S. aureus isolates were found to produce precipitin halos on the antiserum agar. The percentage was greatest in the isolates from the endocarditis group (100%) and least in deep tissue infections (55.5%). The presence of clinical S. aureus strains producing exopolysaccharides antigenically identical to the Smith diffuse strain exopolysaccharide appears to be a common phenomenon.