Recombinant Omp2b antigen-based ELISA is an efficient tool for specific serodiagnosis of animal brucellosis

Control of brucellosis as a worldwide zoonotic disease is based on vaccination of animals and diagnosis of infected cases to be eradicated. Accurate and rapid detection of infected animals is of critical importance for preventing the spread of disease. Current detection of brucellosis is based on whole-cell antigens and investigating serum antibodies against Brucella lipopolysaccharide (LPS). The critical disadvantage is misdiagnosis of vaccinated animals as infected ones and also cross-reactions with other Gram-negative bacteria. Recombinant outer membrane protein 2b (Omp2b) of Brucella abortus was evaluated as a novel serodiagnostic target in comparison to conventional tests which are based on LPS. Recombinant Omp2b (rOmp2b) was expressed in Escherichia coli BL21 and purified by Ni²⁺-based chromatography. rOmp2b was evaluated in an indirect enzyme-linked immunosorbent assay (ELISA) system for diagnosis of brucellosis, with sera from Brucella-infected mice along with negative sera and sera from mice which were inoculated with other Gram-negative species for assurance of specificity. Thereafter, cattle sera collected from different regions were assessed along with known negative and known positive serum samples. We found that Omp2b can discriminate between Brucella-infected animals and non-infected ones. Results for assessment of two hundred and fifty cattle sera by Omp2b-based indirect ELISA which were compared to Rose Bengal plate agglutination test (RBPT) and serum tube agglutination test (SAT) showed that our proposed procedure has the sensitivity of 88.5%, specificity of 100%, and accuracy of 90.8%. We suggest that recombinant Omp2b could be used as a protein antigen for diagnosis of brucellosis in domestic animals and can be evaluated for detection of human brucellosis.