InlA Promotes Dissemination of Listeria monocytogenes to the Mesenteric Lymph Nodes during Food Borne Infection of Mice

Abstract

Intestinal Listeria monocytogenes infection is not efficient in mice and this has been attributed to a low affinity interaction between the bacterial surface protein InlA and E-cadherin on murine intestinal epithelial cells. Previous studies using either transgenic mice expressing human E-cadherin or mouse-adapted L. monocytogenes expressing a modified InlA protein (InlAm) with high affinity for murine E-cadherin showed increased efficiency of intragastric infection. However, the large inocula used in these studies disseminated to the spleen and liver rapidly, resulting in a lethal systemic infection that made it difficult to define the natural course of intestinal infection. We describe here a novel mouse model of oral listeriosis that closely mimics all phases of human disease: (1) ingestion of contaminated food, (2) a distinct period of time during which L. monocytogenes colonize only the intestines, (3) varying degrees of systemic spread in susceptible vs. resistant mice, and (4) late stage spread to the brain. Using this natural feeding model, we showed that the type of food, the time of day when feeding occurred, and mouse gender each affected susceptibility to L. monocytogenes infection. Co-infection studies using L. monocytogenes strains that expressed either a high affinity ligand for E-cadherin (InlAm), a low affinity ligand (wild type InlA from Lm EGDe), or no InlA (ΔinlA) showed that InlA was not required to establish intestinal infection in mice. However, expression of InlAm significantly increased bacterial persistence in the underlying lamina propria and greatly enhanced dissemination to the mesenteric lymph nodes. Thus, these studies revealed a previously uncharacterized role for InlA in facilitating systemic spread via the lymphatic system after invasion of the gut mucosa.

Intracellular Listeria monocytogenes Comprises a Minimal but Vital Fraction of the Intestinal Burden following Foodborne Infection

“…The mouse-adapted strain of L. monocytogenes is ideal for studying oral transmission of listeriosis in mice because it can be used at doses that are 10-to 100-fold lower than the 10 9 CFU typically required to establish intestinal infection with wild-type L. monocytogenes EGDe (3,15). However, Tsai et al recently showed that the InlA m protein expressed by the mouse-adapted strain altered the tropism for L. monocytogenes in the intestinal epithelium by promoting binding to N-cadherin as well as E-cadherin (16).…”

“…However, as a facultative intracellular pathogen, L. monocytogenes can readily survive and multiply in extracellular spaces, and there may be multiple environments that harbor extracellular bacteria during infection. For example, we previously showed that extracellular L. monocytogenes was present in the lamina propria of both the ileum and the colon after foodborne infection (3). The liver, spleen, and placenta were each shown to contain gentamicin-sensitive L. monocytogenes during systemic infection of mice or guinea pigs (4,5).…”

“…Wollert et al constructed a mouse-adapted L. monocytogenes strain expressing a modified InlA protein (InlA m ) that binds murine E-cadherin with a similar affinity as native InlA binds human Ecadherin (15). Using this mouse-adapted strain, intestinal infection can be established with doses as low as 10 6 to 10 7 CFU in susceptible animals (3,15). Tsai et al recently reported that the mouse-adapted L. monocytogenes strain has an altered cell tropism for intestinal invasion compared to infection in the E16P humanized mice, but it is not entirely clear how that may affect dissemination to the MLN during foodborne infection (16).…”

The Listeria monocytogenes Hibernation-Promoting Factor Is Required for the Formation of 100S Ribosomes, Optimal Fitness, and Pathogenesis

“…For intravenous infections, 200 l of bacterial suspension in PBS (Gibco) was administered by injection into the tail vein. Oral infections were carried out as previously described (26). Briefly, bacteria were suspended in melted butter and applied to 0.5-cm cubes of white bread.…”

IL-17A–producing resident memory γδ T cells orchestrate the innate immune response to secondary oral Listeria monocytogenes infection

“…At early time points following oral infection, recombinant L. monocytogenes invades intestinal mucosa and is later detected in the MLNs before it spreads systemically (15). Thus, we primarily focused our study on investigating γδ T cells that reside in the gutdraining MLNs.…”