Determination of resistance and virulence gene profiles
The panel of genes encoding resistance to the following antimicrobials was analysed: tetracycline [tet A, tet B], aminoglycosides [aph (3′ )-Iaand aph (3′ )-IIa], [str A], [aac (3)-II,aac (3)-III], phenicols [cml A, cat, flo R], and sulphonamides [sul 1, sul 2, sul 3]. In order to determine the pathotypes of the strains, the following virulence genes were amplified: genes encoding adhesins [afa/draBC, ea-I, papAH, sfa/foc, papC, bfp ], toxins [stx1, stx2, STa, STb, hlyA, eltA ], iron acquisition systems [iutA ], serum resistance [kpsMTII ], and miscellaneous factors [escV ].
All amplification reactions were carried out in the thermal cycler (T100™ Thermal Cycler, Bio Rad, Hercules, California, USA) using PCR Mix Plus (A&A Biotechnology, Gdynia, Poland), the GoldTaq mix (Syngen Biotech, Poland), and 1-µl DNA sample. The sequence of appropriate primers and reaction conditions (Genomed, Warsaw, Poland) used in this study are described in Table S1.