The gut microbiome of critically ill individuals and its modification by immunonutrition and probiotics

In a recent review published in the Nutrients Journal, researchers reviewed existing evidence on gut dysbiosis among critically ill individuals and the re-establishment of microbial diversity in the gut by probiotics and immunonutrition in the severely diseased population.

Study: Gut Microbiota and Critically Ill Patients: Immunity and Its Modulation via Probiotics and Immunonutrition. Image Credit: MeekoMedia/Shutterstock.com

Background

Critically ill individuals experience hyperinflammation due to injuries, leading to tissue injury, organ failure, and mortality. Research on gut dysbiosis in intensive care units (ICUs) could help develop personalized treatment strategies.

Probiotic supplementation and immunontrition can attenuate inflammation, particularly in postoperative infections and ventilation performance. However, further research is required to improve the understanding of their impact on critically ill health.

About the review

In the present review, researchers described the gut microbiome of critically ill individuals and its modulation by probiotics and immunonutrition.

The study based on data obtained from databases such as Scopus, and the National Center for Biotechnology Information (NCBI) PubMed, including reviews, experimental studies, and retrospective analyses, published in English.

Gut microbiota in critically ill patients

Gut microflora in non-ICU patients include phyla such as Bacteroidetes, Firmicutes, Actinobacteria, Proteobacteria, Fusobacteria, and Verucomicrobia, and genera such as Lactobacillus, Clostridium, Enterococcus, Bacteroides, Streptococcus, Pseudomonas, Prevotella, Corynebacterium, Actinomyces, Acinetobacter, Akkermansia, Bifidobacterium, and Fusobacterium.

ICU patients have a particular type of intestinal dysbiosis that results from and also perpetuates hyperinflammation. Key molecules involved in the hyperinflammation developed in response to tissue injury include damage-associated-pattern molecules (DAMPS) and pathogen-associated pattern molecules (PAMPS).

Anti-inflammatory medications such as immunosuppressants, non-steroidal anti-inflammatory drugs, and steroids can lower the cytokine-induced hyperinflammation in coronavirus disease 2019 (COVID-19) patients; however, they may be insufficient to prevent tissue injury.

Gut dysfunction involves damage to the intestines of critically ill individuals, impacting the intestinal epithelium, immune system, and composition of the gut microflora. Gut dysbiosis, including altered levels of gut metabolites such as trimethylamine N-oxide and short-chain fatty acids (SCFAs), can significantly impact the inflammatory responses of an individual.

Hypoperfusion and reperfusion of the intestinal wall of critically ill individuals can increase mucosal inflammation, gut permeability, nitrate concentrations, and lower oxygen concentrations. Hyperinflammation is associated with significant decreases in the total organic acid, acetic acid, and butyric acid content, and an increase in fecal pH, which favour the growth of gram-negative, facultative, and obligate anaerobic, lipopolysaccharide (LPS)-producing pathogens.

Among ICU patients, there is an increased abundance of pathogenic microbes such as Bacteroidetes, Firmicutes, Actinobacteria, and Proteobacteria, with a decrease in Verucomicrobia, and Fusobacteria species.

ICU patients have demonstrated an increased abundance of microbes such as Clostridium, Lactobacillus, Enterococcus, Bacteroides, Streptococcus, Pseudomonas, Prevotella, Corynebacterium, Acinetobacter, Bifidobacterium, and Actinomyces. In contrast, microbes such as Fusobacterium, Akkermansia, and Faecalibacterium have lowered abundance among critically ill patients.

Use of probiotics and immunonutrition among critically ill individuals

Critically ill individuals have depressed immunological surveillance and, conversely, a hyper-inflammatory state, which increases malnutrition and mortality risks. Intestinal dysfunction can influence the prognosis of individuals suffering from shock, sepsis, trauma, bleeding, and burning.

Particular food nutrients, administered via the parenteral or enteral routes, can influence gut microbiota composition.

Probiotics refer to live microorganisms that benefit the host. Studies have reported that probiotics can reduce diarrhea incidence, significantly enhance natural killer cell activity and lymphocyte count, and lower the levels of pro-inflammatory cytokines such as interleukin-6 (IL-6).

Probiotic use has also significantly reduced the incidence rates of ventilator-associated pneumonia (VAP), infectious complications, and deaths.

Probiotics used among critically ill individuals include Streptococcus thermophiles, L. casei, L. bulgaricus, L. rhamnosus GG, Saccharomyces boulardii, B. longum, S. boulardii, Bifidobacterium breve, Lactobacillus casei, Pediococcus, Lactobacillus, Bifidobacterium lactis, Bacillus subtilis, Streptococcus, Leuconostoc, Bifidus, Ergyphilus, Enterococcus, and Saccharomyces species.

Other microbes utilized for probiotic supplementation among critically ill individuals include Lactobacillus acidophilus, Lactobacillus paracasei, Lactobacillus helveticus, Lactobacillus brevis, and Lactobacillus plantarum.

Gut dysbiosis is associated with immunological dysfunction characterized by lowered B and T lymphocyte counts, involving pathogen recognition receptors (PPARs), such as nucleotide oligomerization domain (NOD)-like receptors (NLRs), and toll-like receptors (TLRs) in the gut.

Immunontrition refers to the modulation of immunological activity or the implications of immunological activation by particular foods and includes casein, vitamins A, C, and D, microelements such as selenium and zinc, omega-3 fatty acids, and phytochemicals such as curcumin and flavonoids.

Immunontrition can lower intestinal inflammation in pediatric IBD patients and has reduced the incidence of sepsis, systemic inflammatory response syndrome (SIRS), multiple organ failure (MOF), and sarcopenia when used before and after surgery.

Among ICU-admitted COVID-19 patients, immunontrition can lower cytokine levels and prevent malnutrition development.

Based on the review findings, probiotics and immunonutrition have promising potential for improving the health status of critically ill individuals by modulating their gut microbiome and suppressing the associated hyperinflammation.

Written by

Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.