Friend or foe: the gut microbiota as a modulator of disease trajectory in trauma, surgery, and critical illness.

The connections between host physiology and the gut microbiome continue to grow as we learn how both the composition and function of the microbiota can impact organ systems beyond the gastrointestinal tract (e.g. the liver, lungs, kidneys, brain). An individual's unique life history plays an important role in shaping the gut microbiota, whose composition and functional output may influence the clinical course and outcomes following a major physiologic perturbation such as surgery or trauma in a manner that extends beyond host genetics. Alterations in the gut microbiota that occur during the course of an illness may explain some of the heterogeneity seen in both recovery and the development of complications. Here, we challenge traditional perspectives on infectious complications, in which pathogenic strains of bacteria are considered to be the sole perpetrators. In this review, we instead examine the crosstalk between the pathogen, the host, and its colonizing microbiome - termed the "interactome"-and explore its role in driving disease progression or recovery following major physiologic perturbations including surgery, trauma, and critical illness.