Occurrence of Yersinia enterocolitica O:9 in feces from cows seropositive for brucellosis

The diagnosis of brucellosis is mainly based on serological tests. All animals classified as serologically positive are obligatorily slaughtered and subjected to bacteriological examination. B. abortus has not been reported in Poland since the eradication of bovine brucellosis in 1980. On the other hand, B. suis biovar 2 is sporadically isolated from cattle. In accordance with the instructions of the Chief Veterinary Officer, samples of feces from animals slaughtered following positive serological results for brucellosis have been examined for the presence of Yersinia enterocolitica O:9 since 2011. Because of the similarity of its O-polysaccharide component of S-LIPS with that of Brucella, this microorganism is considered to be a major contributory factor of false positive serological reactions (FPSR). The paper presents the results of the bacteriological and molecular examination of feces from 26 cows seropositive for brucellosis and 30 healthy cows, negative for brucellosis, for the presence of Y. enterocolitica O:9. Y. enterocolitica O:9 was found in 7 of the positive cows, whereas all samples from cows negative for brucellosis were free from this bacteria. These results indicate that Y. enterocolitica O:9 may be responsible for some of the positive results for brucellosis in cattle.