The Gut-as-Motor of MODS Revisited: Dysbiosis-Driven Multi-Organ Dysfunction in Critical Illness

Critical illness triggers rapid gut microbiome dysbiosis and intestinal barrier disruption, transforming the gut from a regulated symbiotic organ into a sustained source of pathogen- and damage-associated molecular patterns (PAMPs/DAMPs) that drive multiple organ dysfunction syndrome (MODS). Splanchnic hypoperfusion during circulatory shock, catecholamine-mediated vasoconstriction, and reperfusion injury degrade epithelial tight junctions, deplete the protective mucus layer, and facilitate bacterial translocation. Commensal depletion eliminates short-chain fatty acids (SCFAs) and aryl hydrocarbon receptor (AhR) ligands, depriving colonocytes of their preferred energy substrate and impairing immune tolerance through loss of regulatory T cell differentiation. Four interlinked mechanistic pathways—increased permeability and translocation, SCFA deficiency, AhR/tryptophan depletion, and immune tolerance collapse—converge into a self-perpetuating vicious cycle linking gut injury to systemic organ failure. Clinical studies associate dysbiosis severity, pathogenic overgrowth (particularly Enterococcus and Pseudomonas species), and elevated intestinal permeability biomarkers with prolonged mechanical ventilation, secondary infections, and mortality; however, alpha diversity loss alone is not significantly associated with mortality, and taxon-specific abundance may be more prognostic. Therapeutic strategies—including microbiota-preserving antimicrobial stewardship, fiber-enriched early enteral nutrition, SCFA supplementation, selective digestive decontamination, and probiotics—show mechanistic promise but require multicenter randomized validation. Reconceptualizing the gut microbiome as the motor of MODS identifies actionable therapeutic targets during the first two weeks of critical illness.