Methodological aspects of Staphylococcus aureus peptidoglycan serology: comparisons between solid-phase radioimmunoassay and enzyme-linked immunosorbent assay.

In the present studies we compared the ability of two commonly used assays, solid-phase radioimmunoassay and enzyme-linked immunosorbent assay (ELISA), to detect human antibodies to Staphylococcus aureus peptidoglycan. ELISA was superior, with a reproducibility of 12.0%, as compared with 18.1% in solid-phase radioimmunoassay. Much lower serum dilutions could be used in ELISA. We also studied the effects of solubilizing the antigen by lysostaphin, lysozyme, or ultrasonication. Lysostaphin-treated peptidoglycan cannot be recommended since solid-phase radioimmunoassay could not distinguish positive from negative serum samples with this preparation. On the other hand, the sensitivity in both assays was high when peptidoglycan treated with lysozyme for 240 min or with ultrasonication for 30 min was used as antigen. The interassay correlation between solid-phase radioimmunoassay and ELISA was slightly better with sonicated peptidoglycan (correlation coefficient = 0.94, P less than 0.01), as compared with lysozyme-treated peptidoglycan (correlation coefficient = 0.76, P less than 0.01). We recommend the ELISA with sonicated peptidoglycan as antigen for use in routine serology.