Mosaic structure of Shiga-toxin-2-encoding phages isolated from Escherichia coli O157 : H7 indicates frequent gene exchange between lambdoid phage genomes

Shiga-toxin-2 (sfx(2))-encoding bacteriophages were isolated from Norwegian Escherichia coli 0157:H7 isolates of cattle and human origin. the phages w ere characterized by restriction enzyme analysis, hybridization with probes for toxin genes and selected phage DNA such as the P gene, integrase gene and IS1203, and by PCR studies and partial sequencing of selected DNA regio ns in the integrase to stx(2) region of the phages. The stx(2)-phage-contai ning bacteria from which inducible phages were detected produced similar am ounts of toxin, as shown by a Vero cell assay. The results indicate that th e population of stx(2)-carrying phages is heterogeneous, although the phage s from epidemiologically linked E. coli 0157:H7 isolates were similar. Ther e appears to have been frequent recombination of stx(2) phages with other l ambdoid phages.