Zebrafish (Danio rerio) as a vertebrate model host to study colonization, pathogenesis and transmission of food-borne Escherichia coli O157: Zebrafish model of food-borne EHEC O157 infection

Food-borne infections with enterohemorrhagic Escherichia coli (EHEC) are a major cause of diarrheal illness in humans and can lead to severe complications such as hemolytic uremic syndrome. Cattle and other ruminants are the main reservoir of EHEC, which enters the food chain through contaminated meat, dairy, or vegetables. Here, we describe the establishment of a vertebrate model for food-borne EHEC infection, using larval zebrafish (Danio rerio) as a host and the protozoan prey Paramecium caudatum as a vehicle. We follow pathogen release from the vehicle, intestinal colonization, microbe-host interactions, and microbial gene induction within a live vertebrate host, in real-time, throughout the course of infection. We demonstrate that food-borne EHEC colonize the gastrointestinal tract faster and establish a higher burden compared to water-borne infection. Expression of the Locus of Enterocyte Effacement (LEE), a key EHEC virulence factor, was observed early during infection, mainly at sites that experience fluid shear, and required tight control to enable successful host colonization. EHEC infection led to a strain- and LEE-dependent mortality in the zebrafish host. Despite the endogenous microbiota limiting EHEC colonization levels, EHEC colonization and virulence can be studied either under gnotobiotic conditions or against the backdrop of an endogenous (and variable) host microbiota. Finally, we show that the model can be used for investigation of factors affecting shedding and transmission of bacteria to naïve hosts. Overall, this constitutes a useful model, which ideally complements the strengths of existing EHEC vertebrate models.