Listeria monocytogenes (Lm) is a food-borne pathogen that causes severe bacterial gastroenteritis, with high rates of hospitalization and mortality. Lm is ubiquitous in soil, water and livestock, and can survive and proliferate at low temperatures. Following oral ingestion of contaminated food, Lm crosses the epithelial through intestinal goblet cells in a mechanism depending on Lm InlA and host E-cadherin. Importantly, human infections typically occur with Lm growing at or below room temperature, which are flagellated and motile. Even though many important human bacterial pathogens are flagellated, little is known regarding the effect of bacterial motility on invasion and immune evasion.
Here, we used complementary imaging and computer modeling approaches to test the hypothesis that bacterial motility helps Lm locate and engage target cells permissive for invasion. Imaging explanted mouse and human intestine, we confirmed that Lm grown at room temperature uses motility to scan the epithelial surface and preferentially attach to target cells. Furthermore, we integrated quantitative parameters from our imaging experiments to construct a versatile “layered” cellular Potts model (L-CPM) that simulates host-pathogen dynamics. Simulated data are consistent with the hypothesis that bacterial motility enhances invasion by allowing bacteria to search the epithelial surface for their preferred invasion targets. Indeed, our model consistently predicts that motile bacteria have invaded ∼2-fold more at the 1-hour mark. This invasion advantage persists even in the presence of host phagocytes, with the balance between invasion and phagocytosis governed almost entirely by bacterial motility.
In conclusion, our simulations provide insight into host pathogen interactions and challenge fundamental assumptions regarding how phagocytes might limit bacterial invasion early during infection.