Sheep were inoculated with an E. coli O157:H7 strain containing an Stx2-encoding bacteriophage (Phi3538) in which a chloramphenicol-resistant gene, cat, is inserted into stx(2). A total of 149 faecal samples were sampled and analysed for detection and quantification of E. coli O157:H7 and presumptive transductants. Phage Phi3538 (Deltastx(2)::cat) was demonstrated to be transduced to an ovine E. coli O175:H16 at one occasion.