Enzyme immunoassay of the capsular polysaccharide of Streptococcus pneumoniae type III in cerebrospinal fluid in experimental meningitis.

An enzyme immunoassay (EIA) for the capsular polysaccharide of Streptococcus pneumoniae type III was developed and applied to the measurement of this antigen in cerebrospinal fluid (CSF) in an experimental model of pneumococcal meningitis. EIA was performed by a single-antibody sandwich technique in which the globulin fraction of pneumococcal type-specific antiserum (antiserum-globulin) was used to coat the solid phase before antigen attachment and to conjugate with the labelling enzyme, horseradish peroxidase. Under optimum assay conditions EIA detected purified pneumococcal type-III capsular polysaccharide in concentrations as low as 0.15 ng/ml in aqueous buffer. Assayed by EIA, the mean concentration of type-III capsular polysaccharide in CSF of rabbits with pneumococcal meningitis increased exponentially from 24 h to 96nh of infection (range 13.9 ng/ml--62 500 ng/ml). Effective antimicrobial therapy of rabbits with meningitis was associated with a rapid decrease in the CSF concentration of the capsular antigen, although it was still detected in concentration in the range 1--10 ng/ml in 100% of animals treated for 4 days. Thus EIA provides a quantitative and extremely sensitive method of measuring type-III pneumococcal capsular polysaccharide in CSF.