Mouse models for bacterial enteropathogen infections: insights into the role of colonization resistance

Abstract

Globally, enteropathogenic bacteria are a major cause of morbidity and mortality.^1-3 Campylobacter, Salmonella, Shiga-toxin-producing Escherichia coli, and Listeria are among the top five most commonly reported zoonotic pathogens in the European Union.⁴ However, not all individuals naturally exposed to enteropathogens go on to develop disease. This protection is attributable to colonization resistance (CR) conferred by the gut microbiota, as well as an array of physical, chemical, and immunological barriers that limit infection. Despite their importance for human health, a detailed understanding of gastrointestinal barriers to infection is lacking, and further research is required to investigate the mechanisms that underpin inter-individual differences in resistance to gastrointestinal infection. Here, we discuss the current mouse models available to study infections by non-typhoidal Salmonella strains, Citrobacter rodentium (as a model for enteropathogenic and enterohemorrhagic E. coli), Listeria monocytogenes, and Campylobacter jejuni. Clostridioides difficile is included as another important cause of enteric disease in which resistance is dependent upon CR. We outline which parameters of human infection are recapitulated in these mouse models, including the impact of CR, disease pathology, disease progression, and mucosal immune response. This will showcase common virulence strategies, highlight mechanistic differences, and help researchers from microbiology, infectiology, microbiome research, and mucosal immunology to select the optimal mouse model.

Figure 1.

Known mechanisms inhibiting enteropathogen growth in the gut. The resident microbiota in the gut of mammals protects their host from pathogens via mechanisms including the production of short-chain fatty acids (SCFAs), the secretion of bacteriocins, the conversion of primary into secondary bile salts, and the competition for nutrients from the host diet. In addition, phages restrict the colonization of invading bacteria. Finally, a fast transit time makes it challenging for a pathogen to colonize the gut and intestinal epithelial cells (IECs) secrete antimicrobial peptides and IgA antibodies. It is not known if all of the mechanisms indicated are relevant to every enteropathogen.

Figure 2.

Comparison of the infection process at the intestinal epithelium between the five enteropathogens. The red inhibition arrow indicates the reduction in CR against the pathogen if the pathogen can trigger gut inflammation.