Project Summary The movement of enteric bacteria from the intestine to the blood and other organs is called translocation, a concept recognized clinically in the 1960s and defined experimentally in the 1980s. Translocation is a major precursor to the development of life-threatening bacteremia and sepsis, with a compromised immune system being a dominant risk factor. A significant cause of gut-derived sepsis is ExPEC, which clinically is the most frequently isolated Gram-negative pathogen from bacteremic patients. ExPEC is often multi-drug resistant, and there is evidence that such strains may be chronic colonizers of the GI tract. There is no vaccine. The mechanism by which ExPEC translocates out of the intestine has not been determined, and the bacterial factors needed for this process remain unknown. This funding period proposes to determine the importance of the pilus tip adhesin FimH in translocation. Preliminary data presented here suggests FimH is required for clinical strains of ExPEC to bind, invade, and pass through a transformed intestinal cell line. Hypothesizing that FimH is necessary for translocation in human hosts, we test here the requirements of FimH for passage through human intestinal enteroids and translocation in a murine model of leukopenia. In addition, we use these model systems, which our laboratory developed, to determine the molecular requirements of FimH-mediated translocation through enterocytes, the importance of FimH in globally circulating lineages of ExPEC, and if distinct FimH alleles dictate the efficiency of translocation. This work will determine if FimH is a viable target for preventing gut-derived sepsis in high-risk patients.