Severely injured traumatic brain injury TBI patients who appear otherwise equivalent upon admission, will classically dichotomize into those who survive without life-threatening complications and those who develop organ dysfunction andor sepsis. Some evidence indicates that variants of specific genes are associated wpoor outcomes following severe trauma however, the relationships between gene expression and clinical consequences are unknown. Considering the evidence that the human gut microbiome plays an important role in many diseases, studies are needed to determine how changes in the gut microbiota following severe trauma may affect outcomes. This project will deliver key information regarding divergent patient responses to severe TBI, wthe potential to offer personalized approaches to therapeutics and supportive care, decreased early mortality and improved long-term functional outcome. Given the proportionately excessive incidence of TBI among members of the US military, the concepts and approaches tested by this project should have a particularly high impact on the men and women of our armed services.