CHARACTERIZATION OF A MONOCLONAL-ANTIBODY SPECIFIC FOR BRUCELLA SMOOTH LIPOPOLYSACCHARIDE AND DEVELOPMENT OF A COMPETITIVE ENZYME-LINKED-IMMUNOSORBENT-ASSAY TO IMPROVE THE SEROLOGICAL DIAGNOSIS OF BRUCELLOSIS

The reactivity of monoclonal antibody (MAb) 12G12 was analyzed in rega rd to the main biovars of Brucella species and some members of the fam ilies Enterobacteriaceae and Vibrionaceae which present serological cr oss-reactions with the smooth lipopolysaccharide (S-LPS) of Brucella s pecies. This MAb was strictly directed against the common specific epi tope of the Brucella S-LPS. It recognized all of the smooth Brucella s trains and biovars except B. suis biovar 2. In order to improve the sp ecificity of the serological diagnosis of brucellosis, a competitive e nzyme-linked immunosorbent assay (cELISA) was developed with the horse radish peroxidase-conjugated MAbs 12G12 and S-LPS of B. melitensis Rev 1. The specificity of the cELISA was analyzed with 936 serum samples f rom healthy cattle. The assay was evaluated with sera from heifers (n = 18) experimentally infected with B. abortus 544. After infection, th e performance of the cELISA was in agreement with those of the complem ent fixation test and the rose Bengal plate test. Finally, the specifi city of the assay was also evaluated in regard to false-positive serol ogical reactions by using sera from heifers experimentally infected wi th Yersinia enterocolitica O:9 (n = 4) and with field sera presenting false-positive reactions (n = 74). The specificity of the cELISA was g reater than the specificities of the complement fixation test and the rose Bengal plate test. Indeed, the new assay detected only 31 of the 101 false-positive serum samples detected by at least one serological test.