A total of 200 Escherichia coli isolates recovered from milk secrets of acute mastitis of cows were examined for virulence factors commonly found in pathogenic groups of E coli, O-serotypes and resistance to 17 therapeutic drugs. The genes of 26 virulence factors were detected by polymerase chain reaction and the E coli O-serogroups were assessed by agglutination tests using poly- and mono-specific antisera. Drug resistance was tested and evaluated using MIC assay (SENSITITRE-TOUCH-SYSTEM, NETHERLANDS). Out of 200 mastitic isolates, 81 % showed at least one of tested genes, of these 76.5 % had fimH, 33 % traT, 14 % each hlyD and fyuA, 11 % cnf1, 8.5 % iutA, 6.5 % Pal, 6 % each cdtB and papA, 4.5 % cvaC, 4 % cnf2, 1.5 % each stx and AIDA-1 genes sequence, 1 % eaeA, and 0.5 % each f1711, afaD-8 and afaE-8. Most of the genes were distributed in combinations. The genes for f17 family a-d, afaD-7, afaE-7 and sfaS were not detected. The presence of toxins (cnf1, cnf2, stx(1), stx(2), cdtB) and intimin (eaeA) encoding genes was demonstrated in 24.5 % of strains and distributed among 22 % of cattle herds analysed. E coli strains of this study belonged to 12 O-serogroups including: O25, O26, O55, O78, O103, O114, O119, O125, O126, O128, O145, and O157. 52.5 % of all strains were resistant to one or two antimicrobial agents whereas further 17.5 % showed multiple drug resistance.