Postnatal development of the small intestinal mucosa drives age-dependent, regio-selective susceptibility to Escherichia coli K1 infection.

The strong age dependency of neonatal systemic infection with Escherichia coli K1 can be replicated in the neonatal rat. Gastrointestinal (GI) colonization of two-day-old (P2) rats leads to invasion of the blood within 48 h of initiation of colonization; pups become progressively less susceptible to infection over the P2-P9 period. We show that, in animals colonized at P2 but not at P9, E. coli K1 bacteria gain access to the enterocyte surface in the mid-region of the small intestine and translocate through the epithelial cell monolayer by an intracellular pathway to the submucosa. In this region of the GI tract, the protective mucus barrier is poorly developed but matures to full thickness over P2-P9, coincident with the development of resistance to invasion. At P9, E. coli K1 bacteria are physically separated from villi by the mucus layer and their numbers controlled by mucus-embedded antimicrobial peptides, preventing invasion of host tissues.

Non-invasive model of neuropathogenic Escherichia coli infection in the neonatal rat.

Investigation of the interactions between animal host and bacterial pathogen is only meaningful if the infection model employed replicates the principal features of the natural infection. This protocol describes procedures for the establishment and evaluation of systemic infection due to neuropathogenic Escherichia coli K1 in the neonatal rat. Colonization of the gastrointestinal tract leads to dissemination of the pathogen along the gut-lymph-blood-brain course of infection and the model displays strong age dependency. A strain of E. coli O18:K1 with enhanced virulence for the neonatal rat produces exceptionally high rates of colonization, translocation to the blood compartment and invasion of the meninges following transit through the choroid plexus. As in the human host, penetration of the central nervous system is accompanied by local inflammation and an invariably lethal outcome. The model is of proven utility for studies of the mechanism of pathogenesis, for evaluation of therapeutic interventions and for assessment of bacterial virulence.

Altered innate defenses in the neonatal gastrointestinal tract in response to colonization by neuropathogenic Escherichia coli.

Two-day-old (P2), but not 9-day-old (P9), rat pups are susceptible to systemic infection following gastrointestinal colonization by Escherichia coli K1. Age dependency reflects the capacity of colonizing K1 to translocate from gastrointestinal (GI) tract to blood. A complex GI microbiota developed by P2, showed little variation over P2 to P9, and did not prevent stable K1 colonization. Substantial developmental expression was observed over P2 to P9, including upregulation of genes encoding components of the small intestinal (α-defensins Defa24 and Defa-rs1) and colonic (trefoil factor Tff2) mucus barrier. K1 colonization modulated expression of these peptides: developmental expression of Tff2 was dysregulated in P2 tissues and was accompanied by a decrease in mucin Muc2. Conversely, α-defensin genes were upregulated in P9 tissues. We propose that incomplete development of the mucus barrier during early neonatal life and the capacity of colonizing K1 to interfere with mucus barrier maturation provide opportunities for neuropathogen translocation into the bloodstream.