Host-Microbiome Interaction in the Intensive Care Unit

Critical illness profoundly disrupts the gut microbiota leading to a state of dysbiosis characterized by reduced microbial diversity and overrepresentation of pathogenic taxa such as Enterobacteriaceae and Proteobacteria. This dysbiotic shift compromises gut barrier integrity and modulates immune responses, contributing to systemic inflammation and increasing susceptibility to nosocomial infections and multi-organ dysfunction. Nutritional strategies in the ICU significantly influence the composition and function of the gut microbiota. Enteral nutrition supports the maintenance of microbial diversity and gut mucosal health, whereas parenteral nutrition is associated with mucosal atrophy and further microbial imbalance. Emerging interventions, including the administration of probiotics, prebiotics, synbiotics, and fermented products like kefir, show promise in restoring microbial equilibrium and improving patient outcomes. This review presents current evidence on the alterations of the gut microbiota in critically ill patients, explores the systemic consequences of dysbiosis, and evaluates the impact of nutritional and microbiota-targeted therapies in improving patient outcomes.