THE USE OF DIVALENT-CATION CHELATING AGETS (EDTA EGTA) TO REDUCE NONSPECIFIC SERUM-PROTEIN INTERACTION IN ENZYME-IMMUNOASSAY

An indirect enzyme immunoassay (ELISA) for detection of bovine antibod y to Brucella abortus was modified by the addition of divalent chelati ng agents to the serum diluent. This addition resulted in an increase in specificity from 96.0% in the regular assay to 99.4% in the modifie d procedure. Of the 15 715 sera initially tested by the indirect ELISA , 691 that had given positive reactions were selected for retesting in the indirect ELISA with EDTA/EGTA added. The buffered plate antigen t est (BPAT) correctly identified 98.6% of the samples as negative. The addition of chelating agents did not alter the sensitivity of the indi rect ELISA, which correctly classified 609 sera from animals from whic h B. abortus had been isolated as positive. The sensitivity of the BPA T was 97.8%.