EVALUATION OF LIPOPOLYSACCHARIDES AND POLYSACCHARIDES OF DIFFERENT EPITOPIC STRUCTURES IN THE INDIRECT ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR DIAGNOSIS OF BRUCELLOSIS IN SMALL RUMINANTS AND CATTLE

Brucella abortus and Brucella melitensis have surface lipopolysacchari des and polysaccharides carrying B. melitensis-type (M) and B. abortus -type (A) epitopes as well as common (C) epitopes present in all smoot h Brucella biotypes. Crude lipopolysaccharides, hydrolytic O polysacch arides, and native hapten polysaccharides of MC or AC specificity were evaluated in indirect enzyme-linked immunosorbent assays with polyclo nal, monoclonal, or protein G conjugates by using sera from cattle, sh eep, and goats infected with AC, MC, or AMC Brucella biotypes. Regardl ess of the antigen, the levels of antibodies were lower in goats than in sheep and highest in cattle. The diagnostic performance of the assa y was not affected by the absence of lipid A-core epitopes, the presen ce of contaminating outer membrane proteins, the AC or MC epitopic str ucture of the absorbed antigen, or the conjugate used. Moreover, with sera from cattle vaccinated with B. abortus S19 (AC) or from sheep and goats vaccinated with B. melitensis Rev 1 (MC), AC and MC antigens sh owed similar levels of reactivity. The results show that antibodies to the C epitopes largely dominate in infection, and this is consistent with the existence of multiple overlapping C epitopes (V. Weynants, D. Gilson, A. Cloeckaert, A. Tibor, P. A. Denoel, F. Godfroid, J. N. Lim et, and J.-J. Letesson, Infect. Immun. 65:1939-1943, 1997) rather than with one or two C epitopes. It is concluded that, by adaptation to th e corresponding antibody levels, brucellosis in cattle, sheep, and goa ts can be diagnosed by immunosorbent assay with a single combination o f conjugate and antigen.