Prophage Induction Is Enhanced and Required for Renal Disease and Lethality in an EHEC Mouse Model

Abstract

Enterohemorrhagic Escherichia coli (EHEC), particularly serotype O157:H7, causes hemorrhagic colitis, hemolytic uremic syndrome, and even death. In vitro studies showed that Shiga toxin 2 (Stx2), the primary virulence factor expressed by EDL933 (an O157:H7 strain), is encoded by the 933W prophage. And the bacterial subpopulation in which the 933W prophage is induced is the producer of Stx2. Using the germ-free mouse, we show the essential role 933W induction plays in the virulence of EDL933 infection. An EDL933 derivative with a single mutation in its 933W prophage, resulting specifically in that phage being uninducible, colonizes the intestines, but fails to cause any of the pathological changes seen with the parent strain. Hence, induction of the 933W prophage is the primary event leading to disease from EDL933 infection. We constructed a derivative of EDL933, SIVET, with a biosensor that specifically measures induction of the 933W prophage. Using this biosensor to measure 933W induction in germ-free mice, we found an increase three logs greater than was expected from in vitro results. Since the induced population produces and releases Stx2, this result indicates that an activity in the intestine increases Stx2 production.

Role of bacteriophages in STEC infections: new implications for the design of prophylactic and treatment approaches

“…Tyler and collaborators recently showed that prophage induction is required for renal disease and lethality in the EHEC mouse model, suggesting that free bacteriophages encoding Stx may play a direct role in the disease 3 .…”

“…Recently, it was reported that bacteriophages carrying the stx gene are required for the development of HUS in the murine model 3 . We hypothesise that eukaryotic host cells might be transduced with and/or infected by Stx-encoding bacteriophages, leading to Stx dissemination in vivo to enter the systemic circulation.…”

Impact of Spontaneous Prophage Induction on the Fitness of Bacterial Populations and Host-Microbe Interactions

“…In the proposed model, a small fraction of cells induces the Stx-encoding prophages, leading to Shiga toxin release and, in consequence, priming the gut epithelial cells by the expression and relocation of nucleolin and further receptors to the epithelial cell surface. These receptors were previously shown to bind to the bacterial surface protein intimin, thus promoting STEC colonization (77)(78)(79). In these bacteria, expression of a type 3 secretion system (T3S), which is required for colonization, was shown to be influenced by the presence of Stx-encoding prophages.…”

Shiga toxins and stx phages: highly diverse entities

“…This switch from the lysogenic state to the lytic state is called induction. Thus, expression of stx in STEC depends primarily on prophage induction (Wagner et al, 2001;Tyler et al, 2013), although stx 1 transcription can be also driven by its own promoter under low iron conditions (Calderwood & Mekalanos, 1987;Aertsen et al, 2005b).…”

“…Moreover, Tyler et al (2013) showed that Stx2 production and disease in an enterohaemorrhagic E. coli mouse model were directly related to induction of the 933W prophage. However, the stx phage characteristics that contribute to both high virulence and variation in disease severity are poorly understood.…”