Virulence properties of Shiga toxin-producing Escherichia coli isolated from cases of bovine mastitis in Brazil

Out of 528 milk samples obtained from dairy cows with mastitis, 31 (5.8%) had Escherichia coli strains, causative agent of mastitis. These strains were screened for the presence of Shiga toxin-producing (stx1 and stx2) and intimin (eae) genes. Twenty (64.5%) strains were detected by PCR to harbor the Shiga toxin genes (13 the stx1 gene, 3 the stx2 gene, and 4 the stx1-stx2 genes). Three (9.6%) of the E. coli strains studied were eae positive non Shiga toxinproducing. The E. coli strains were also examined for resistance to 15 antimicrobial agents. The most commonly observed resistance was to novobiocin (100%), lincomycin (96.8%), penicillin (96.8%) and erythromycin (90.3%). All the strains tested showed resistance to at least one antimicrobial agent and multidrug resistance was very common (96.8%).