SIMULTANEOUS IDENTIFICATION OF ANTIBODIES TO BRUCELLA-ABORTUS AND STAPHYLOCOCCUS-AUREUS IN MILK SAMPLES BY FLOW-CYTOMETRY

Two flow cytometric assays are described herein. The single cytometric test (SCT) detects antibodies to either Brucella abortus or Staphyloc occus aureus in the serum or milk of a cow or water buffalo. The doubl e cytometric test (DCT) detects both anti-B. abortus and anti-S. aureu s antibodies concurrently. In the SCT, the sample to be tested is incu bated in succession with the antigen (either B. abortus or S. aureus) and the proper secondary antiserum (fluorescein isothiocyanate-labelle d rabbit anti-cow immunoglobulin antiserum or rabbit anti-water buffal o immunoglobulin antiserum). In the DCT, the sample to be tested is in cubated first with B. abortus and S. aureus antigens and then with the secondary antiserum. The B. abortus antigen used in the DCT is covale ntly bound to 3-mu m-diameter latex particles. The difference in size between B. abortus and S. aureus permits the establishment of whether the antibodies are directed against one, the other, or both antigens. When compared to the complement fixation test, the SCT and DCT each sh ow a specificity and a sensitivity of 100%. The SCT has been used prev iously to detect anti-S. aureus antibodies. Here its use is extended t o the detection of anti-B. abortus antibodies. The DCT is described he re for the first time. The DCT appears to be useful for large-scale br ucellosis eradication programs. It offers the possibility of using one test to identify animals that are serologically positive for both B. abortus and S. aureus.