Substitution of anti-human globulin by protein A-bearing staphylococci in the detection of Brucella antibodies.

A coagglutination test using protein A-bearing staphylococci has been developed for the detection of Brucella antibodies. Comparing the results of a random sample of 57 sera collected from Malta fever patients, suggestive titers of 1: greater than or equal to 160 were found in 8 sera (14%) with the standard agglutination test, in 22 sera (39%) with the Coombs test, and in 23 sera (40%) with the coagglutination test. The titers in the Coombs test and the coagglutination test coincided in 54 (95%) of the 57 sera, in 3 sera (5%) the difference was no more than one dilution step. Sera from healthy subjects and patients with infections other than brucellosis showed titers up to 1:40 in all three tests. Because of its sensitivity and specificity in detecting non-agglutinating antibodies, the Brucella-antibody coagglutination test may replace the Coombs test as a complementary assay to the standard agglutination. Native sera from Malta fever patients frequently show a prozone phenomenon in the standard agglutination test and a reduced agglutinate formation in both the Coombs test and the coagglutination test. The inhibitors of agglutination lattice formation are apparently serum beta-lipoproteins which become attached to the Brucella antigen and can be removed from the serum by treatment with MnCl2-heparin.