The Role of the Gut Microbiota in Sepsis: Evidence from the SURVEIL Project

Sepsis is a life-threatening condition frequently associated with gut dysbiosis and bacterial colonization by multidrug-resistant (MDR) organisms. However, the interplay between gut microbiota, colonization patterns, and sepsis onset remains poorly defined. The authors analyzed longitudinal gut microbiota profiles from 132 hospitalized patients enrolled in the SURVEIL study. Rectal swabs were collected at three time points (baseline, sepsis onset, and discharge). Bacterial colonization status and MDR strains were determined through culture-based methods, while microbiota composition was assessed via 16S rDNA sequencing. Diversity indices, taxonomic and functional profiles, and differential abundance analyses (LEfSe) were integrated with clinical metadata, including age and sepsis status. At baseline, colonized patients—particularly those harboring Gram-positive taxa—exhibited significantly reduced alpha diversity compared to non-colonized individuals. Aging further modulated diversity and beta diversity patterns independently. Sepsis was associated with profound dysbiosis, characterized by enrichment in opportunistic genera (e.g., Finegoldia sp., Anaerococcus sp., Parabacteroides sp.), reduced microbial diversity, and distinct beta diversity trajectories. Functional predictions revealed enhanced representation of anaerobic metabolism, nitrogen/sulfur cycling, and host-adaptive traits in colonized states. MDR strains partially overlapped with bloodstream pathogens in septic patients, suggesting a potential gut-origin for systemic infection. Our findings demonstrate that bacterial colonization and sepsis are strongly associated with compositional and functional shifts in the gut microbiota. Age and MDR carriage further shape microbiota dynamics. Early microbial signatures, such as Finegoldia sp. enrichment in colonized non-septic patients, may represent early markers of microbial destabilization and sepsis risk. Gut microbiota profiling may support predictive strategies and guide microbiota-sparing interventions in critical care.