ABSTRACTCytolethal distending toxin (Cdt) is produced by a variety of pathogenic bacteria, including pathogenic serotypes of Shiga toxin-producingEscherichia coli(STEC). The Cdt family comprises five variants (Cdt-I to Cdt-V) encoded by three genes located within the chromosome or plasmids or, in the case of Cdt-I, within bacteriophages. In this study, we evaluated the occurrence of thecdtgene in a collection of 140 environmental STEC isolates.cdtwas detected in 12.1% of strains, of which five strains carried inducible bacteriophages containing the Cdt-V variant. Two Cdt-V phages of theSiphoviridaemorphology lysogenizedShigella sonnei, generating two lysogens: a single Cdt phage lysogen and a double lysogen, containing a Cdt phage and an Stx phage, both from the wild-type strain. The rates of induction of Cdt phages were evaluated by quantitative PCR, and spontaneous induction of Cdt-V phage was observed, whereas induction of Stx phage in the double lysogen was mitomycin C dependent. The Cdt distending effect was observed in HeLa cells inoculated with the supernatant of the Cdt-V phage lysogen. A ClaI fragment containing thecdt-Vgene of one phage was cloned, and sequencing confirmed the presence of Cdt-V, as well as a fragment downstream from thecdthomolog togpA, encoding a replication protein of bacteriophage P2. Evaluation of Cdt-V phages in nonclinical water samples showed densities of 102to 109gene copies in 100 ml, suggesting the high prevalence of Cdt phages in nonclinical environments.
Bacteriophage P2
