Gut Microbiota Alterations Associated With Colonization by Multidrug-Resistant Organisms in ICU Patients: First Systematic Review and Meta-Analysis

Abstract

Colonization by multidrug-resistant organisms (MDROs) is a risk factor for infection and mortality in critically ill patients, yet current strategies to prevent or control dissemination show variable effectiveness. Whether alterations in microbiota structure and composition (dysbiosis) are associated with MDRO colonization in critically ill patients is an open question this study aims to address. We conducted the first systematic review and meta-analysis comparing intestinal microbiota structure (diversity) and composition (relative abundance of bacteria) between colonized critically ill patients and noncolonized/control patients. PubMed, Web of Science, and Scopus were systematically searched from inception to September 2025. The study protocol was preregistered on Open Science Framework, under embargo. Of 3003 records identified, 11 studies (n = 2823 patients) published between 2019 and 2025 met the inclusion criteria. The most frequently reported colonizing strains in MDROs-colonized patients were vancomycin-resistant Enterococci (58.2%), carbapenem-resistant Enterobacterales (21.6%), extended-spectrum β-lactamase–producing Enterobacterales (13.4%). All studies employed 16S ribosomal RNA sequencing to assess intestinal microbiota. Colonized critically ill patients had lower values of dominance/evenness and richness, reaching significantly lower values of information when compared with controls (mean difference in Shannon index = –1.18; 95% CI, –1.84 to –0.52; p < 0.001). Composition investigation revealed a significant increase in the Pseudomonadota phylum and the Enterobacteriaceae family in MDROs-colonized patients. Current evidence is limited and largely associational. Nevertheless, altered intestinal microbiota consistently characterize colonized critically ill patients. Further studies are warranted to determine whether early detection of dysbiosis can enhance early prediction/diagnosis of MDROs-colonization and guide the targeted microbiota-based strategies to prevent infections.