ATTEMPTED DEFINITION BY IMMUNOBLOTTING OF THE CAUSES OF REACTIVITY INSUSPECTED FALSE-POSITIVE SERA IN THE BRUCELLA-OVIS COMPLEMENT-FIXATION TEST

Seventy-nine suspected false-positive sera, obtained over 1 year from routine submissions for Brucella ovis serological testing, were used i n this study. These sera; which exhibited titres in the complement fix ation test, but which because of their epidemiological history and the ir reactions in the enzyme-linked immunosorbent assay and gel diffusio n test were suspected to be false positives, were further analysed by immunoblotting. In blots, using B. ovis antigens, rough lipopolysaccha ride was identified as the major, immune-reactive bacterial component. Antibodies against this macromolecule were present in 46.8% of the su spected false-positive sera. In order to fmd out if rough lipopolysacc harides from other bacterial species could be the possible cause for t he suspected false positivity, 23 sera with highest complement fixatio n titres were reacted in blots with cell extracts from Escherichia col i, Yersinia enterocolitica, Yersinia pseudotuberculosis, Bortedella br onchiseptica, Actinobacillus seminis, Campylobacter fetus fetus, Campy lobacter jejuni, Mycobacterium paratuberculosis, Mycobacterium phlei, Corynebacterium pseudotuberculosis and pure lipopolysaccharides from E scherichia coli and Salmonella typhimurium. Despite high frequencies o f antibody reaction with proteins in most of these bacterial cell extr acts, which reflect the presence of infections with these bacteria, im mune-staining in the rough lipopolysaccharide region was not observed.