EN
A total of 192 pig tonsils were examined for the presence of Yersinia enterocolitica rods. Y. enterocolitica was isolated from 25 (13.02%) pig tonsil samples collected from various herds in Northeast Poland. All isolates, except for one which was not typeable, were found to belong to biotypes 4 (60%) and 1A (36%). The PCR product of 747 bp, resulting from the amplification of the plasmid-borne yadA gene fragment, was detected in 14 biotype 4 isolates with CRMOX-positive phenotype. The PCR products of 356 bp, corresponding to the ail gene fragment, and of 134 bp, corresponding to the ystA gene fragment, were detected in all the tested isolates belonging to biotype 4. The isolates of biotype 1A and the untypeable isolate gave the PCR product of 69 bp, corresponding to the ystB gene fragment. All of the Y. enterocolitica isolates gave a positive PCR reaction for the myfA gene. All Y. enterocolitica isolates were susceptible to cefotaxime, imipenem, tetracyclines, and aminoglycosides and susceptible or moderately susceptible to norfloxacin. All the isolates were resistant to amoxicillin and most of them were resistant to cefazolin. In comparison to biotype 4 isolates, which were all susceptible to amoxicillin/clavulan, in biotype 1A 55.6% of the isolates were resistant to this combination. The present study supports the hypothesis that swine represent a potential reservoir for Y. enterocolitica strains which are possibly pathogenic for humans.