Shiga toxin-producing Escherichia coli (STEC) are emerging pathogens worldwide. Infections associated with STEC have a broad clinical spectrum from asymptomatic infections, acute diarrhea, dysenteric diarrhea and Hemolytic Uremic Syndrome. Some serotypes of STEC are highly virulent for humans due to the presence of two cytotoxins (Stx1, Stx2) and a pathogenicity island called Locus of Enterocyte Effacement (LEE), which is responsible for the adherence to intestinal epithelium, mainly through the intimin protein encoded by eae gene. Other factors have been implicated in virulence, e.g., the products of the efa1, iha, hylA, lpf and saa genes, which are encoded in the genomes of O157 and non-O157. In Chile, STEC Non-O157 serogroups are the most important cause of STEC infections. It has been found that the presence of these specific genes is more relevant than is that of the serogroup. In Chile, a high rate of STEC isolations in swine and bovines as asymptomatic carriers has been reported. Therefore the Chilean Ministry of Health has incorporated STEC as an agent under surveillance. Recently, samples from swine and bovines at slaughter were analyzed and, interestingly, only the bovine carrying STEC exhibited the virulence genes found in human isolates. Several strategies have been proposed to prevent STEC colonization in the animal host, where findings following vaccination with proteins from the LEE locus are encouraging. Thus,, DNA vaccines have been used as a novel strategy, and the immunized animals have shown a strong lymphocyte proliferation against bacterial antigens.