Limitations of the BP26 Protein-Based Indirect Enzyme-Linked Immunosorbent Assay for Diagnosis of Brucellosis

Brucellosis is a serious zoonosis that occurs worldwide, and its diagnosis is typically based on the detection of antibodies againstBrucella lipopolysaccharide (LPS). However, the specificity of the LPS-based test is compromised by cross-reactivity withEscherichia coli O157:H7 andYersinia enterocolitica O:9. Also, diagnosis based on the LPS test cannot differentiate between vaccinated and infected individuals. The detection of the 26-kDa cytosoluble protein (BP26) antibody is considered an alternative that circumvents these drawbacks because it is exclusively expressed by infectiousBrucella . A BP26-based enzyme-linked immunosorbent assay (ELISA) has been tried for the diagnosis ofBrucella -infected animals and humans, but a few results showed that BP26 couldn't react with allBrucella -positive sera. In order to explore whether different animals could produce antibodies against BP26 after being infected with variousBrucella species, we infected sheep, goats, and beef cattle with common virulent referenceBrucella species. All sera were collected from the experimental animals and tested using both LPS-based ELISAs and BP26-based ELISAs. The results showed that allBrucella -infected individuals could produce high levels of antibodies against LPS, but onlyB. melitensis 16M- andB. melitensis M28-infected sheep andB. melitensis 16M- andB. abortus 2308-infected goats could produce antibodies against BP26. Therefore, we concluded that the BP26-based indirect ELISA (i-ELISA) showed bothBrucella species and host specificity, which obviously limits its reliability as a substitute for the traditional LPS-based ELISA for the detection of brucellosis.