Muc2 mucin limits Listeria monocytogenes dissemination and modulates its population dynamics
The mucin Muc2 is a major constituent of the mucus layer that covers the intestinal epithelium and creates a barrier between epithelial cells and luminal commensal or pathogenic microorganisms. The Gram-positive food-borne pathogen Listeria monocytogenes can cause enteritis and also disseminate from the intestine to give rise to systemic disease. L. monocytogenes can bind to intestinal Muc2, but the influence of the Muc2 mucin barrier on L. monocytogenes intestinal colonization and systemic dissemination has not been explored. Here, we used an orogastric L. monocytogenes infection model to investigate the role of Muc2 in host defense against L. monocytogenes. Compared to wild-type mice, we found that Muc2-/- mice exhibited heightened susceptibility to orogastric challenge with L. monocytogenes, with higher mortality, elevated colonic pathology, and increased pathogen burdens in both the intestinal tract and distal organs. In contrast, L. monocytogenes burdens were equivalent in wild-type and Muc2-/- animals when the pathogen was administered intraperitoneally, suggesting that systemic immune defects do not explain the heightened pathogen dissemination observed with oral infection route. Using a barcoded L. monocytogenes library to measure intra-host pathogen population dynamics, we found that Muc2-/- animals had larger pathogen founding population sizes in the intestine and distal sites than observed in wild-type animals. Comparisons of barcode frequencies revealed that, in the absence of Muc2, the colon becomes the major source for seeding the internal organs. Together, our findings reveal that Muc2 limits L. monocytogenes dissemination from the intestinal tract and modulates its population dynamics during infection.