TABLE 1.

Summarized data from a comparison of microplate assay protocolsa

Fold increase in titerNo. of individuals with indicated titer increase
Original protocolModified protocol
<2189
2-<437
≥438
  • a Paired serum samples from O139 vaccine recipients (n = 24) were tested for bactericidal antibodies by two microplate assay protocols, involving either saline diluent and indicator bacteria at 3 × 106 per ml (original protocol) or Mg2+-saline diluent and indicator bacteria at 105 per ml (modified protocol). For both methods, the streptomycin-resistant strain 4260B was used as the indicator strain; assays were read spectrophotometrically, and 70% killing endpoints were determined. The data indicate the numbers of individuals registering various titer increases according to each procedure.