Efficacy of several serological tests and antigens for diagnosis of bovine brucellosis in the presence of false-positive serological results due to Yersinia enterocolitica O:9.

Yersinia enterocolitica O:9 bears a smooth lipopolysaccharide (S-LPS) of Brucella sp. O-chain A+C/Y epitopic structure and is a cause of false-positive serological reactions (FPSR) in standard tests for cattle brucellosis. Brucella S-LPS, cross-reacting S-LPSs representing several O-chain epitope combinations, Brucella core lipid A epitopes (rough LPS), Brucella abortus S-LPS-derived polysaccharide, native hapten polysaccharide, rough LPS group 3 outer membrane protein complexes, recombinant BP26, and cytosolic proteins were tested in enzyme-linked immunosorbent assays (ELISA) and precipitation tests to detect cattle brucellosis (sensitivity) and to differentiate it from FPSR (specificity). No single serological test and antigen combination showed 100% sensitivity and specificity simultaneously. Immunoprecipitation tests with native hapten polysaccharide, counterimmunoelectrophoresis with cytosolic proteins, and a chaotropic ELISA with Brucella S-LPS were 100% specific but less sensitive than the Rose Bengal test, complement fixation, and indirect ELISA with Brucella S-LPSs and native hapten or S-LPS-derived polysaccharides. A competitive ELISA with Brucella S-LPS and M84 C/Y-specific monoclonal antibody was not 100% specific and was less sensitive than other tests. ELISA with Brucella suis bv. 2 S-LPS (deficient in C epitopes), Escherichia hermannii S-LPSs [lacking the contiguous alpha-(1-2)-linked perosamine residues characteristic of Y. enterocolitica S-LPS], BP26 recombinant protein, and Brucella cytosolic fractions did not provide adequate sensitivity/specificity ratios. Although no serological test and antigen combination fully resolved the diagnosis of bovine brucellosis in the presence of FPSR, some are simple and practical alternatives to the brucellin skin test currently recommended for differential diagnosis.