Innate immunity restricts Citrobacter rodentium A/E pathogenesis initiation to an early window of opportunity

Abstract

Citrobacter rodentium infection is a mouse model for the important human diarrheal infection caused by enteropathogenic E. coli (EPEC). The pathogenesis of both species is very similar and depends on their unique ability to form intimately epithelium-adherent microcolonies, also known as “attachment/effacement” (A/E) lesions. These microcolonies must be dynamic and able to self-renew by continuous re-infection of the rapidly regenerating epithelium. It is unknown whether sustained epithelial A/E lesion pathogenesis is achieved through re-infection by planktonic bacteria from the luminal compartment or local spread of sessile bacteria without a planktonic phase. Focusing on the earliest events as C. rodentium becomes established, we show here that all colonic epithelial A/E microcolonies are clonal bacterial populations, and thus depend on local clonal growth to persist. In wild-type mice, microcolonies are established exclusively within the first 18 hours of infection. These early events shape the ongoing intestinal geography and severity of infection despite the continuous presence of phenotypically virulent luminal bacteria. Mechanistically, induced resistance to A/E lesion de-novo formation is mediated by TLR-MyD88/Trif-dependent signaling and is induced specifically by virulent C. rodentium in a virulence gene-dependent manner. Our data demonstrate that the establishment phase of C. rodentium pathogenesis in vivo is restricted to a very short window of opportunity that determines both disease geography and severity.

Uncoupling of invasive bacterial mucosal immunogenicity from pathogenicity

“…Quantitation of cecal luminal lipocalin-2 and histopathology scores both confirmed the protective effects of STm Aux treatment within each mouse genotype ( Supplementary Fig. 11B, C), although these two readouts themselves are MYD88/TRIF-dependent 17,34 and should therefore be compared between both mouse genotypes with caution.…”

Tandem tyrosine residues in the EPEC multicargo chaperone CesT support differential type III effector translocation and early host colonization

“…We set out to investigate whether specific C-terminal CesT tyrosines are important for bacterial intestinal colonization and disease in a natural mouse infection model for A/E pathogenesis. C. rodentium has been widely used by researchers to assess the role of its putative virulence factors in mice, including many aspects of its cognate T3SS and numerous effectors (8, 38–41). Importantly C. rodentium cesT null mutants have been shown to be strongly attenuated for mouse intestinal colonization and disease (8).…”

“…We did observe that C. rodentium (CesT F152, F153) did replicate within mice, but was cleared from the mouse colon more rapidly than wild type C. rodentium . Recently, it has been demonstrated that the establishment phase of C. rodentium pathogenesis in vivo is restricted to a very short window of opportunity (~18 hours) that determines intestinal intimate attachment and disease severity (41). Indeed, our data directly agree with those findings in that bacteria expressing CesT F152, F153 were attenuated for F-actin pedestal formation (EPEC) and mouse intestinal infection ( C. rodentium ).…”

<i>Citrobacter rodentium</i>, a Gut Pathogen: The Yin and the Yang of Its Pathophysiology, Immunity and Clinical Manifestation in Mice

“…Following entry to the body via oral route, C. rodentium colonizes the caecal patch, a type of lymphoid tissue in caecum, from where the bacteria gradually progress to colonise distal colon [17] [18] [19]. For colonization, the bacteria triggers localised damage of brush border microvilli, which mediates bacteria to attach to the epithelial cell surface.…”

“…The only means that are currently available to address this limitation include transgenic strains of C. rodentium that express OVA or GFP [96] [97] [98]. Another probable limitation to study this pathogen could be the loss of antibiotic sensitivity of C. rodentium due to the development of worldwide emergence of multi-resistant strains [19].…”