Cryptosporidium spp. are opportunistic protozoan parasites that infect epithelial cells of the small intestine, causing diarrheal illness in humans. In immunodeficient individuals, the disease can be severe, chronic and even fatal. In both adults and children, the disease can range from asymptomatic to severe. These differences in susceptibility and disease severity are known to be due in part to immunological status of the host, malnutrition, or prior exposure. But one important factor that has had limited study, is the role microbiota plays in host resistance. While differences in microbiota have been linked to susceptibility, it is not clear which bacterial microbiota profiles are important in resistance and which might pre-dispose individuals to infections or to more severe disease. It is also not understood how altered microbiota changes the metabolic profile in the intestinal tract and how this impacts the immune response of the host. Our long-term goal is to understand the underlying gut environment and how that may be related to susceptibility and severity of infection. Our objective is to determine how differences in microbiota affect resistance and susceptibility to infections and to determine if overall patterns or profiles can be identified. Additionally, we plan to determine if there is an association between changes in bacterial metabolites and infection levels. The central hypothesis in this proposal is that differences in the microbiota alter susceptibility and host immune response to C. parvum infection which allow for greater expansion of the organism. We will test this hypothesis by treating mice with different antibiotics and a repurposed drug known to alter the intestinal flora and examine how these changes affect susceptibility, infection level, and host immune responses, particularly activation of T cells and cytokine response in the local environment. The rationale for this hypothesis is based on the our preliminary data that show that there are significant changes in the microbiome of mice treated with certain antibiotics compared to vehicle control mice, which results in increased susceptibility. Additionally, metabolic analyses will be performed to determine changes in short chain fatty acid levels, amino acids and lipids. We will correlate difference in metabolites to susceptibility and growth. These changes may subsequently alter the immune response and microbiota-associated metabolites that result in modulation of local T cells and secretion of key cytokines, such as IFN-?. These findings would be significant because it would help advance the understanding of mechanisms underlying the expansion of cryptosporidiosis during conditions of increased vulnerability. In addition, by identifying microbiota profiles in individuals that are at greater risk of infection (e.g immunodeficient individuals, transplant recipients, and young children), interventions could be administered to bolster or alter the microbiota to a more resistant profile.
The proposed research is relevant to the NIH mission because cryptosporidiosis is the second major cause of diarrheal illness in children globally and can be severe and life threatening in immunocompromised individuals (e.g. HIV-infected). Currently, there is no vaccine and only 1 drug that is FDA approved for immunocompetent individuals Understanding the role the microbiome plays in susceptibility and resistance to infection may lead to preventive or therapeutic treatment strategies for these vulnerable populations.