Stwierdzenie obecności chromosomalnych markerów wirulencji takich jak: geny ail i yst oraz brak zdolności do wytwarzania pyrazynamidazy, fermentacji salicyny i hydrolizy eskuliny mogą być wykorzystywane do identyfikowania chorobotwórczych szczepów Y. enterocolitica, które utraciły plazmid wirulencji pYV.
It is well known that virulent strains of Y. enterocolitica bear the virulence-associated plasmid pYV. Moreover some authors consider that the pathogenic strains of these bacteria have chromosome encoded phenotypic and genotypie features such as: genes ail and yst which could be used as virulence markers. The virulent strains of Y. enterocolitica do not produce pyrasinamidase and are not able to ferment salicin and cannot hydrolyse esculin. In addition these strains produce thermostable enterotoxin called YST and protein Ail (attachment invasion locus). In contrast to phenotypic virulence makers the biological function of proteins Ail, YST and nucleotide sequence of genes ait and yst is well described. In the presented study one hundred thirty virulence plasmid bearing Y. enterocolitica strains beloging to serogorup 03 were examined for the presence of genes ail, yst, and were tested for their inability to pyrasinamidase production, salicin fermentation and esculin hyrolysis. In addition forty pYV plasmid-cured isogenic strains were included in to the study. Genes ail and yst were detected by polymerase chain reaction (PCR). The obtained results indicate that all tested 130 pYV+ Y. enterocolitica strains as well as 40 plasmid-cured isogenic strains have carried ail and yst genes. All tested strains did not produce pyrasinamidase, hydrolyse esculin and ferment salicin. This generally was in agreement with the observations done by other authors and suggest that the chromosomal virulence markers, especially well described genes ail and yst, could be useful for excluding the potential virulence of Y. enterocolitica strains, which bad lost pYV plasmid and have no ail or yst genes. Therefore, in clinical studies, Y. enterocolitica strains isolated directly from patients should be primarily tested for the presence of the virulence plasmid and secondarily, the negative ones could be examined for the presence of the chromosomal virulence markers.