Technical aspects of the Staphylococcus aureus teichoic acid antibody assay: gel diffusion and counterimmunoelecrophoretic assays, antigen preparation, antigen selection, concentration effects, and cross-reactions with other organisms

Abstract

Because variable results are being reported from laboratories performing the teichoic acid antibody assay in patients with serious infections due to Staphylococcus aureus, we have thoroughly reviewed all technical aspects of the test. This paper reports on the importance of agar and antigen preparation in standardizing results of the assay and reducing the prevalence of false-negative and -positive tests. Once standardized, the counterimmunoelectrophoretic method is as accurate as the gel diffusion method for both initial screening and generating titers; practically, however, unless numerous tests are to be performed, the gel diffusion technique will suffice for most purposes. The cell wall of the Lafferty strain of S. aureus was used as the standard antigen in assays for serum antibodies. We studied whether it is an appropriate antigen and found that antibody titers obtained with the Lafferty strain antigen were, in three patients with endocarditis, the same as those obtained with antigens from the individual blood stream isolates. We have also confirmed that pooled human gamma globulin can be used, by back titration against newly prepared lots of antigen, to select optimal antigen concentration and is as good as more specific, higher titer serum specimens for that purpose. Finally, cell wall antigens from Staphylococcus epidermidis and a variety of streptococci may react with normal human sera, but such antigens are distinct by immunoprecipitation from those from S. aureus.