EN
The aim of this study was the characterization of Staphylococcus aureus strains isolated from milk of cows with mastitis in the north-east region of Poland. Genotyping of 45 isolates by ADSRRS-fingerprinting showed nine different patterns of bands. Genotype D was predominant and 29 S. aureus strains (65.5%) were classified to this genotype. These strains of genotype D had strong pathogenicity, because in the first year of the study only 14.29% isolates belonged to D and in the next year 73.64% isolates. The strains of the predominant genotype showed stronger pathogenic properties then the strains of other genotypes. The majority of them showed a significant adhesion to the epithelial cells of the mammary gland, and the strong ability to produce slime and to form biofilm.