The aim of the study was to perform a molecular investigations for the presence of pathogenicity genotypic markers of Y.enterocolitica O:9 isolated from cattle, in which initially positive serological reactions for brucellosis were observed. Almost all isolates were ail-, ystA- and myfA-positive (n=19). On the other hand, one isolate, which harboured plasmid encoding gene yadA was ail- , ystA- and myfA-negative. The plasmid encoding yadA marker was present in half of the isolates tested. None of the examined isolates was ystB-positive. The results of the investigations revealed that the Y. enterocolitica O:9 isolates, related to false positive serological results for brucellosis, may be also potentially pathogenic for humans, due to the presence of chromosomal and plasmidencoded molecular markers.
