Retrospective analysis of intestinal flora alterations in adults with acute gastrointestinal injury

Background Acute Gastrointestinal Injury is a common and serious complication in critically ill adults associated with poor outcomes. Its progression involves intestinal barrier dysfunction, nutritional impairment, and gut microbiota alterations, which remain inadequately characterized across severity grades. Objective This study aimed to evaluate the association between gut microbiota composition, nutritional status, clinical severity, and outcomes. Methods A retrospective cross-sectional study of 550 adults with AGI (grades I–IV) and controls was conducted across multiple tertiary hospitals from June to September 2025, including 343 males. Clinical, nutritional, biochemical, and microbiota data were analyzed by AGI severity using diversity measures and multivariate regression models. Results Increasing AGI severity was associated with age, higher comorbidity burden, greater illness severity, increased organ support requirements, and worse clinical outcomes, including prolonged ICU stay and higher mortality (p < 0.001). Severe AGI (III–IV) patients showed pronounced gastrointestinal dysfunction, delayed and interrupted enteral nutrition, reduced caloric adequacy, and significantly impaired nutritional biomarkers. Marked gut dysbiosis was observed with increasing AGI severity, characterized by significantly reduced microbial diversity, depletion of beneficial taxa ( Firmicutes, Bacteroidetes, Lactobacillus, Bifidobacterium, Faecalibacterium ), and overgrowth of potentially pathogenic bacteria, particularly Proteobacteria and Escherichia–Shigella (all p < 0.001). Multivariate analysis identified higher age, APACHE II and SOFA scores, antibiotic and proton pump inhibitor use, and interruption of enteral nutrition as independent risk factors associated with severe AGI and dysbiosis, whereas higher BMI, serum albumin levels, and greater microbial diversity were associated with a lower likelihood of severe AGI. Conclusion AGI severity is closely associated with worsening intestinal dysbiosis, deteriorating nutritional status, and poorer clinical outcomes. These findings highlight the importance of early nutritional support and microbiota-targeted interventions in managing critically ill AGI patients.