A systems-level approach to probe the effect of a high- fat/high-protein diet in Clostridioides difficile infection

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PROJECT SUMMARY Clostridioides (formerly Clostridium) difficile infection (CDI) is the leading cause of healthcare-associated and antibiotic-associated infections in all age groups in North America. In the U.S., there are ~500,000 cases of CDI annually, and over 25,000 deaths per year are attributed to CDI. CDI prevention and treatment costs the healthcare system an estimated $6.3 billion/year. The predominant risk factor for CDI is the use of broad-spectrum antibiotics and can be directly attributed to disruption of the intestinal microbiome. Diet also exerts strong controls on the structure and function of the gut microbiome; however, the role of diet in CDI risk and severity is not well understood. Existing reports are contradictory regarding the effects of diet on CDI. We have conducted initial experiments on the effect of diet on CDI using a mouse model of antibiotic-associated CDI. Strikingly, our studies showed that mice fed a high-fat/high-protein, Atkins-like diet suffered 100% mortality, whereas mice fed a high-carbohydrate diet developed few or no signs of disease. In this proposal, we will test the hypothesis that a combination of host and pathogen responses to a high-fat/high-protein diet, within the context of a depleted microbiome, together promote an environment conducive to C. difficile pathogenesis. In Specific Aim 1, we will determine whether the high-fat/high-protein diet, alone or in combination with antibiotics, induces inflammation and increased intestinal permeability prior to exposure to C. difficile. We will also document changes in lumen metabolites and assess CDI severity and mortality compared to an improved matched- ingredient, high-carbohydrate diet. In Specific Aim 2, we will probe the structure and function of the microbiome using both metagenomics and metatranscriptomics at each stage of the experiment (diet only, diet plus antibiotics, diet plus antibiotics and CDI) to explore the hypothesis that antibiotic treatment leads to the absence of a few specific competitors for amino acids that leads to an open niche for C. difficile overgrowth. We will also specifically examine relationships between the C. difficile transcriptome and changes in metabolite pools to delineate two different metabolic states that define CDI outcome, leading to either fulminant CDI and mortality and an asymptomatic carrier state. As a result of this project, we will have a better understanding of the influence of diet, particularly high-fat/high-protein diets, on the host and microbiome and how these diets mediate fulminant CDI. A positive impact would eventually be better management of diet in high-risk individuals, especially during antibiotic treatments, and possible pre- or probiotics for CDI. 1