SEROLOGICAL CROSS-REACTIVITY BETWEEN BRUCELLA-ABORTUS AND YERSINIA-ENTEROCOLITICA 0 9 .2. THE USE OF YERSINIA OUTER PROTEINS FOR THE SPECIFIC DETECTION OF YERSINIA-ENTEROCOLITICA INFECTIONS IN RUMINANTS/

Yersinia outer protein (YOP) preparations from Y. enterocolitica and Y . pseudotuberculosis were used as antigens in immunoblots for the dete ction of Yersinia infections in experimentally and naturally infected ruminants. Sera from 9 groups of animals were used: (1) 51 sera from c attle which were false-positive in the standard brucellosis serologica l tests, (2) 52 sera from brucellosis-negative cattle, (3) 51 sera fro m a deer herd in which 16 animals were positive in the brucellosis tes ts and Yersina species were isolated from 5 animals, (4) 50 sera from a deer herd in which sera from all animals were negative in the brucel losis tests, (5) 107 sera from brucellosis-negative cattle which were received from throughout New Zealand, (6) 30 sera from cattle naturall y infected with B. abortus and from which B. abortus was isolated, (7) 55 sera from cattle naturally infected with B. abortus, (8) 26 sera f rom cattle experimentally infected with B. abortus, with mostly high t itres in the conventional brucellosis tests, and (9) sera taken weekly from 3 cattle experimentally infected with Y. enterocolitica 0:9. In all 3 Y. enterocolitica 0:9 experimentally infected animals the antibo dy reactivity against major YOPs in the Y. enterocolitica and in the Y . pseudotuberculosis YOP preparation correlated well with the strength in the classical brucellosis tests and with the staining of smooth li popolysaccharides (SLPS) in blots, thus confirming the usefulness of Y OPs for the detection of Yersinia infections. Sera from naturally infe cted cattle and deer herds, regardless of whether they were false posi tive or negative in the brucellosis tests, showed high frequencies of staining in YOP blots (53-58% in cattle and 80-100% in deer),indicatin g a high prevalence of field infections with Yersinia species in New Z ealand. In two of the three sera groups from B. abortus infected anima ls, antibodies against YOPs were detected with high frequency, showing that dual infections may be common and may interfere with differentia l serological testing.