Serological Assays against Staphylococcus aureus Peptidoglycan, Crude Staphylococcal Antigen and Staphylolysin in the Diagnosis of Serious S. aureus Infections

Immunoglobulin G antibody levels against Staphylococcus aureus peptidoglycan (PG) and crude staphylococcal antigen (SA) using enzyme-linked immunosorbent assay (ELISA) and antistaphylolysin (ASTA) antibody levels by gel diffusion were determined in 53 patients with S. aureus and 54 patients with non-S. aureus endocarditis and septicemia as compared with 63 febrile control patients. The two ELISAs were the most sensitive assays indicating S. aureus endocarditis in 83% and 88% in the PG- and SA-assays, respectively. 39% of non-S. aureus endocarditis patients were positive in the PG-assay due to antibodies cross-reacting with streptococci. A 100% specificity for S. aureus infections was obtained with the ASTA test, but this assay was less sensitive. A significant rise in anti-PG or anti-SA antibody levels was not only seen among S. aureus infections but also in some streptococcal and S. epidermidis infections as well as in 3 febrile control patients. When at least 2 of the 3 assays showed positive peak antibody levels 1-4 weeks after onset of infection together with a significant rise of both anti-PG and anti-SA antibody levels the S. aureus endocarditis diagnosis was highly suggestive. Thus, we recommend the combined use of these 3 assays using paired serum samples in diagnosing serious S. aureus infections.