The genes encoding the Shiga-like toxins are carried by temperate bacteriophages. We will purify and characterize the temperate bacteriophages present in human and bovine enterohemorragic Escherichia coli (EHEC) strains. The bacteriophage regions flanking the sltII genes will be amplified by IPCR and subsequently the nucleotide sequence of these flanking regions will be determined. These sequences, determined for different bacteriophages, will be compared with know bacteriophage sequences and with each other. This analysis will allow to detect if there is a link between bacteriophages isolated from bovine strains and from human clinical isolates. If there is a link, this information would allow in future to trace the origins of human EHEC strains and to prevent new human infections.