How the metabolic activity of gut bacteria determines the fate of critically ill patients
Imagine that inside each of us exists an entire galaxy inhabited by trillions of living beings. This internal ecosystem — the gut microbiota — doesn't just coexist peacefully with us; it actively participates in maintaining our vital functions. In everyday life, we hardly notice its work, but when the body faces serious illness, injury, or surgery, this delicate balance is disrupted.
Critical illness becomes a test not only for major organs but also for our internal microbial universe. The latest research shows that the metabolic activity of gut bacteria can determine whether a patient survives in the ICU, how quickly they recover, and whether they avoid dangerous complications.
In health, gut microbiota maintains metabolic homeostasis, producing essential metabolites like short-chain fatty acids that regulate inflammation and energy metabolism.
During critical illness, this balance is severely disrupted, leading to dysbiosis that can exacerbate systemic inflammation and organ dysfunction.
In a state of health, the gut microbiota represents a balanced community where approximately 90% of bacteria belong to two main phyla: Bacteroidetes and Firmicutes. These microorganisms perform a vast number of functions: they break down undigested food components, synthesize vitamins, train our immune system, and produce short-chain fatty acids (SCFAs) — crucial metabolites that nourish intestinal epithelial cells and regulate systemic inflammation 2 .
When a person enters the ICU, this well-established system descends into chaos. A condition of dysbiosis develops — a serious disruption in the composition and function of the microbiota. Characteristic changes include:
The intestinal microbiota is recognized as an independent metabolically active organ, — noted in the description of the "Colonoflor-16" test system used to assess the state of microbiocenosis 1 .
Beneficial bacteria normally produce short-chain fatty acids (acetate, propionate, butyrate) from dietary fiber. These substances serve not only as an energy source for intestinal cells but also as important regulators of inflammation. During critical illness, SCFA production sharply decreases, leading to weakening of the intestinal barrier, systemic inflammation, and disruption of immune system function 2 .
| Parameter | Healthy State | Critical State |
|---|---|---|
| Bacterial Diversity | High | Sharply Reduced |
| Dominant Phyla | Bacteroidetes, Firmicutes | Often Proteobacteria |
| Beneficial Bacteria (Faecalibacterium, Bifidobacterium) | Normal | Significantly Reduced |
| Conditional Pathogens (Enterobacteriaceae, Enterococcus) | <1% | Can reach 10-80% |
| SCFA Production | Active | Sharply Reduced |
| Protective Function | Preserved | Impaired |
In 2025, a promising study was published evaluating the safety and efficacy of a strategy aimed at modulating microbiota in patients with chronic critical illness (CCI) 7 . CCI is a special pathological condition that develops in some patients after acute critical illness, when the patient depends on intensive care for more than 14 days.
Dependence on intensive care for
Researchers included 43 patients with CCI and developed an innovative tool — microbiota impairment degree (MID), which integrated seven critically important parameters:
Application of metabiotics (Bactistatin, Actoflor-S)
Metabiotics + selective intestinal decontamination (rifaximin)
Combination of intestine-selective and systemic antimicrobial drugs with metabiotics 7
This approach allowed to minimize pharmacological load on the body while maintaining high treatment efficacy.
The study demonstrated impressive results. Distribution of patients by microbiota impairment degree showed:
| Parameter | Before Intervention | After Intervention | Change |
|---|---|---|---|
| Pneumonia Frequency | High | Significantly Reduced | |
| Inflammatory Markers | Elevated | Reduced | |
| Neurological Status | Various Impairment | Improved | |
| Organ Dysfunction Indicators | Pathological | Trend to Normalization |
Conclusion: These results indicate that targeted impact on microbiota can become a new effective tool in treating the most severe categories of patients.
To investigate the complex metabolic processes of microbiota, researchers use a whole arsenal of modern methods:
Identifies bacteria to genus or species level based on analysis of the conservative gene.
"Shotgun" methods provide information about functional genes of microbial community, including antibiotic resistance genes 2 .
Identification and quantification of metabolites produced by microbiota (SCFAs, tryptophan derivatives, secondary bile acids) 6 .
Although about 80% of microbes are difficult to culture, traditional methods remain useful for some applications.
Advanced computational tools for analyzing complex microbiome datasets and identifying patterns.
Despite encouraging results, researchers face serious challenges. Large randomized controlled trials of pre- and probiotics in critically ill patients have not yet shown consistent benefit 2 . Scientists suggest this may be due to insufficient treatment specificity — not all patients and not at all stages of treatment require the same therapy.
Identifying specific dysbiosis patterns in different categories of ICU patients for targeted interventions.
Uncovering the precise mechanisms by which microbiota influences clinical outcomes in critical illness.
Creating precision treatments that consider the features of microbial ecology in individual patients 2 .
Developing microbiota modulation strategies tailored to individual patient characteristics and disease states.
Of particular interest is the role of microbiota in patients with acute cerebrovascular accidents (stroke). Research shows that patients with stroke and irritable bowel syndrome with predominant constipation have significant changes in the content of bacteria species Akkermansia muciniphila and Prevotella clara 4 . This confirms the importance of the "gut-brain axis" in neurological recovery.
Significantly altered in stroke patients with IBS
Substantial changes observed in neurological patients 4
The study of microbiota metabolism in critical conditions is experiencing a real revolution. From perceiving the gut as simply a digestive organ, we have moved to understanding it as a complex ecosystem, an active metabolic and immune organ on which survival in critical situations may depend.
The gut is now recognized as an active metabolic and immune organ.
Maintaining healthy microbiota may become as important as respiratory support.
Future critical care will include personalized microbiota modulation strategies.
As the authors of the review on the role of microbiota in critical conditions note: "Dysfunction of microbiota can be a predictor and, possibly, the main cause of infectious complications and sepsis" 3 . Understanding this opens new opportunities for saving the most severely ill patients who were previously considered hopeless.