Detection of human serum antibody to encapsulated strains of Staphylococcus aureus by enzyme-linked immunosorbent assay inhibition test.

A specific and rapid enzyme-linked immunosorbent assay (ELISA) inhibition test was employed for detection of immunoglobulins to Staphylococcus aureus (S. aureus) capsular polysaccharide in human serum. Cap-sular polysaccharide antigens obtained from Smith diffuse (capsular type 2), Reynolds (capsular type 5), or Becker (capsular type 8) strains of S. aureus were added to microplates coated with these strains. Seventy-four patients with open fractures (31 serum samples from those with staphylococcal infections, 10 serum samples from those with non-staphylococcal infections, and 33 serum samples from the non-infected group) and 28 serum samples from healthy controls were then added. The plates were incubated at 37 degreesC for 2 h and the ELISA was performed. The ELISA inhibition assay showed remarkable inhibition with the capsular type 2, 5, and 8 polysaccharides in the 33 serum samples from the non-infected group and in the 28 serum samples from the healthy controls, but low inhibition was observed with the 31 sera with staphylococcal infections. Positive immunoglobulin (Ig)G and IgM titers showed marked inhibition with this assay, but IgA titer were not seen in any samples. These results indicate that the quantitation of human serum antibody against S. aureus capsular polysaccharide by the ELISA inhibition assay is useful for the demonstration of protective activities against S. aureus.