Characterization of a shiga toxin 2e-converting bacteriophage from an Escherichia coli strain of human origin

An infectious Shiga toxin (Stx) 2e-converting bacteriophage (phiP27) was isolated from Stx2e-producing Escherichia coli ONT:H(-) isolate 2771/97 originating from a patient with diarrhea. The phage could be transduced to E. coli laboratory strain DH5alpha, and we could show that lysogens were able to produce biologically active toxin in a recA-dependent manner. By DNA sequence analysis of a 6,388-bp HindIII restriction fragment of phiP27, we demonstrated that the stx(2e) gene was located directly downstream of ileZ and argO tRNA genes. Although no analogue of an antiterminator Q encoding gene was present on this fragment, a lysis cassette comprising two holin genes which are related to the holin genes of Pseudomonas aeruginosa phage phiCTX and a gene homologous to the endolysin gene gp19 of phage PS3 were detected. The results of our study demonstrated for the first time that Stx2e can be encoded in the genome of an infectious bacteriophage.