Microbiota Interactions in Critical Illness

Critically ill patients often experience profound disruptions in the communities of microorganisms that reside on and within the human body, collectively known as the microbiota. Factors such as broad-spectrum antibiotics, altered nutrition, mechanical ventilation and organ support therapies contribute to a loss of microbial diversity, favouring overgrowth of opportunistic pathogens. This dysbiosis undermines mucosal barrier integrity, facilitates bacterial translocation and amplifies systemic inflammation. In parallel, the host immune response may become skewed towards ineffective or excessive pathways, further destabilising the balance between microbial communities and host defences. These intertwined disturbances can precipitate nosocomial infections, sepsis, multiorgan dysfunction and prolonged intensive care unit (ICU) stays. Emerging evidence frames the gut microbiota and host immunity as an integrated metasystem, wherein shifts in microbial composition directly influence innate and adaptive immune functions. A clearer understanding of these interactions offers opportunities for diagnostic biomarkers and targeted microbial therapies—ranging from probiotics and prebiotics to precision faecal microbiota transplantation—to restore ecological balance and improve outcomes in critical care settings.

Research from Nature Portfolio

Recent studies have characterised the gut microbiota and systemic immunity as a single interconnected metasystem in critically ill patients. Longitudinal analysis of rectal swabs by 16S rRNA gene sequencing, combined with single-cell mass cytometry profiling of blood immune cells, revealed that enrichment of Enterobacteriaceae correlates with impaired neutrophil function and heightened systemic inflammation. This dysbiotic signature was coupled to a marked increase in hospital-acquired infections across bacterial and fungal species. The work emphasises how alterations in microbial communities can drive defects in innate antimicrobial defences, outlining a mechanistic link between gut dysbiosis and susceptibility to nosocomial infections in the ICU.

Microbiota Interactions in Critical Illness publication trend

The graph below shows the total number of articles in microbiota interactions in critical illness across all publications each year (not limited to Nature Index journals).

Technical terms

Microbiota: The community of microorganisms, including bacteria, fungi and viruses, that inhabit a specific environment, such as the human gut.

Dysbiosis: A pathological imbalance in the composition or function of a microbial community that can contribute to disease.

Metasystem: An integrated network of interacting biological systems, for example the combined gut microbiota and host immune response.

Alpha diversity: A metric reflecting the richness and evenness of species within a single microbial community.

Metagenomics: The study of collective genomes of microbial populations by sequencing DNA directly from environmental samples.

References

1. Dysbiosis of a microbiota–immune metasystem in critical illness is associated with nosocomial infections. Nature Medicine (2023).
2. MASS cohort: Multicenter, longitudinal, and prospective study of the role of microbiome in severe pneumonia and host susceptibility. iMeta (2024).
3. Pathogenesis and therapeutic opportunities of gut microbiome dysbiosis in critical illness. Gut Microbes (2024).