Zebrafish (Danio rerio) as a Vertebrate Model Host To Study Colonization, Pathogenesis, and Transmission of Foodborne Escherichia coli O157

Abstract

Enterohemorrhagic Escherichia coli (EHEC) is a foodborne pathogen which can cause diarrhea, vomiting, and, in some cases, severe complications such as kidney failure in humans. Up to 30% of cattle are colonized with EHEC, which can enter the food chain through contaminated meat, dairy, and vegetables. In order to control infections and stop transmission, it is important to understand what factors allow EHEC to colonize its hosts, cause virulence, and aid transmission. Since this cannot be systematically studied in humans, it is important to develop animal models of infection and transmission. We developed a model which allows us to study foodborne infection in zebrafish, a vertebrate host that is transparent and genetically tractable. Our results show that foodborne infection is more efficient than waterborne infection and that the locus of enterocyte effacement is a key virulence determinant in the zebrafish model. It is induced early during infection, and loss of tight LEE regulation leads to a decreased bacterial burden and decreased host mortality. Overall, the zebrafish model allows us to study foodborne infection, including pathogen release from the food vehicle and gene regulation and its context of host-microbe interactions, as well as environmental shedding and transmission to naive hosts.

The zebrafish as a model for gastrointestinal tract–microbe interactions

“…It is advantageous due to its extremely high throughput and does not require much specialised equipment. More recently, the protozoan Paramecium caudatum, a natural prey for larval zebrafish, has been adapted as a vehicle for foodborne infection models (Fan et al, 2019;Flores et al, 2019;Stones et al, 2017). Immersion cannot be applied to strictly anaerobic microbes.…”

“…Following foodborne delivery via P. caudatum, EHEC colonises the middle intestine of zebrafish larvae despite the presence of endogenous microbiota, and by 4 days post-infection, survival rates decrease by~40% (Stones et al, 2017). Following foodborne delivery via P. caudatum, EHEC colonises the middle intestine of zebrafish larvae despite the presence of endogenous microbiota, and by 4 days post-infection, survival rates decrease by~40% (Stones et al, 2017).…”

“…Following foodborne delivery via P. caudatum, EHEC colonises the middle intestine of zebrafish larvae despite the presence of endogenous microbiota, and by 4 days post-infection, survival rates decrease by~40% (Stones et al, 2017). Following foodborne infection of larval zebrafish, EHEC induces the LEE during early colonisation of the GI tract, and LEE induction is required for optimal colonisation and pathogenesis (Stones et al, 2017). Following foodborne infection of larval zebrafish, EHEC induces the LEE during early colonisation of the GI tract, and LEE induction is required for optimal colonisation and pathogenesis (Stones et al, 2017).…”

“…For some GI pathogens, in particular those for which zebrafish are not a natural host, immersion does not lead to robust intestinal colonisation (e.g., Tysnes, Jørgensen, Poppe, Midtlyng, & Robertson, 2012;Stones et al, 2017 etc.). More recently, the protozoan Paramecium caudatum, a natural prey for larval zebrafish, has been adapted as a vehicle for foodborne infection models (Fan et al, 2019;Flores et al, 2019;Stones et al, 2017). The protozoan internalises bacteria into storage vacuoles, and following uptake of Paramecia by the zebrafish and degradation of the protozoan in the foregut, the bacterial load is released into the middle intestine.…”

“…Another human enteric pathogen successfully modelled in zebrafish is enterohaemorrhagic Escherichia coli (EHEC), which colonises the intestine and causes bloody diarrhoea in the human host. Following foodborne delivery via P. caudatum, EHEC colonises the middle intestine of zebrafish larvae despite the presence of endogenous microbiota, and by 4 days post-infection, survival rates decrease by~40% (Stones et al, 2017). In humans and cattle, intestinal colonisation by EHEC and the formation of attaching and effacing lesions on enterocytes is mediated by a set of virulence genes encoded by the locus of enterocyte effacement (LEE), (Elliott et al, 2000;Phillips et al, 2000).…”