Enzyme-linked immunosorbent assay for measurement of antibody to type III group B streptococci.

Neonates at risk for fulminant type III, group B streptococcal (III GBS) infection are those who lack antibody to the capsular polysaccharide. A newly developed enzyme-linked immunosorbent assay (ELISA) was compared with a standard radioactive antigen-binding assay (RABA) for quantitation of III GBS antibody in human sera. Although there was a significant correlation between the ELISA and RABA (r = 0.81; P less than 0.001) in general, the ELISA detected antibody both to core and native antigens of III GBS, whereas the RABA detected antibody to native polysaccharide exclusively. The results of the two assays were discordant when sera which had only high native or core antibody (not both) were assessed. Although the ELISA was reproducible and required less than 1 microliter of serum, interpretation of data obtained by the assay should be viewed with caution since only antibody to native III GBS has been correlated with human immunity.