Microbiome represents all microorganisms residing on the host (i.e., mouth, lungs, gut, skin) although the majority of bacterial species reside within the gut lumen. The gut microbiome is essential for the development of the gastrointestinal (GI) mucosal immune system, the maintenance of gut homeostasis and for providing essential nutrients (e.g., short chain fatty acids for the intestinal barrier). It also represents a barrier against the colonization of pathogenic microorganisms. Gut microbes are composed by two main phyla (i.e., Firmicutes and Bacteroidetes) [1-4].
Microbiome composition (i.e., type and amount) is modified (i.e., lower bacterial diversity, loss of commensal phyla, and a domination of pathogens or pathobiome, such as Proteobacteria spp.) by factors related with critical illness (i.e., gut hypoperfusion, antibiotics and hyponutrition) that could lead microbiome from normal to opportunistic pathogen overgrowth. Changes in normal microbiome composition is called dysbiosis. Alterations in GI motility (i.e., decreased gastric emptying and gut motility) may enhance bacterial overgrowth in the gut lumen and dysbiosis, which may also enhance systemic inflammatory response and drive distant organ dysfunction [3-6]. Nutrition therapy and supplement therapies (i.e., prebiotics, probiotics, and faecal microbiota transplantation) may be helpful to preserve microbiome composition and function in critically ill [5, 6].
Feasibility/Equipment: The administration of nutrition therapy is crucial for the maintenance of microbiome since gut microbiome depends on the availability of enteral nutrients for survival. Composition of nutrition formula may have positive (e.g., high-fiber composition) or negative (e.g., synthetic dietary emulsifiers and preservatives, such as carboxymethyl cellulose) impact over composition of normal microbiome [5, 6].
On the other hand, to study the composition of gut microbiota, stool samples have to be collected from patients and DNA from stool is isolated. Bacterial gene sequencing techniques and bioinformatics analysis are both necessary for this purpose. Despite obtaining and processing samples is easy for the medical staff, analysis needs complex microbiological and bioinformatic infrastructure [1, 2].
Scoring information: There is not any score or scales to evaluate composition of microbiome.
Cost: The cost of measuring the composition of microbiome is high. However, actions related with appropriate maintenance of normal microbiome are low-cost since most of them are related with the optimization of therapies, such as nutrition administration or antibiotic use, which are currently performed in daily clinical practice by the ICU staff.
Evidence: Inappropriate use of antibiotic (e.g., longer use) and lack of delivery of nutrition therapy by enteral route is associated with higher alterations in microbiome composition, which is closely related with higher number of nosocomial infections and associated-diarrhea in critically ill patients [2-6]. The use of immunontrition (e.g., vitamins, zinc, omega-3 fatty acids, etc.), prebiotics and probiotics may improve the incidence of sepsis, systemic inflammatory response syndrome (SIRS) and multiple organ failure (MOF), especially in surgical patients [5, 6]. Indeed, restoration of the dysbiosis that occurs in critical illness by means of nutrition therapy, prebiotics or probiotics, would have the potential to improve outcomes (i.e., reduce the risk of infections and antibiotic-associated diarrhea) [5-7]. Finally, faecal microbiota transplantation can be indicated for treatment of Clostridium difficile infections [9].
Accuracy / measurement properties: Administration of probiotics have been associated with a reduction in infections (risk ratio from 0.68 to 0.95) and ventilator-associated pneumonia (risk ratio from 0.61 to 0.90) [8]. Probiotics have proven be effective in the prevention and treatment of antibiotic-associated diarrhea (relative risk from 0.50 to 0.68), including Clostridium difficile-associated diarrhea [10]. Despite positive results, evidence is still controversial since scientific literature does not determine which probiotics are associated with the greatest efficacy and which patients benefit the most [2-10].
References
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2. Wozniak H, Beckmann TS, Fröhlich L, Soccorsi T, Le Terrier C, de Watteville A, Schrenzel J, Heidegger CP: The central and biodynamic role of gut microbiota in critically ill patients. Crit Care 2022, 26(1):250.
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4. Sertaridou E, Papaioannou V, Kolios G, Pneumatikos I: Gut failure in critical care: old school versus new school. Ann Gastroenterol 2015, 28(3):309-322.
5. Moron R, Galvez J, Colmenero M, Anderson P, Cabeza J, Rodriguez-Cabezas ME: The Importance of the Microbiome in Critically Ill Patients: Role of Nutrition. Nutrients 2019, 11(12):3002.
6. Abenavoli L, et al: Gut Microbiota and Critically Ill Patients: Immunity and Its Modulation via Probiotics and Immunonutrition. Nutrients 2023, 15(16): 3569.
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9. Limketkai BN, Hendler S, Ting PS, Parian AM: Fecal Microbiota Transplantation for the Critically Ill Patient. Nutr Clin Pract 2019, 34(1):73-79.
10. Hempel S, Newberry SJ, Maher AR, Wang Z, Miles JN, Shanman R, Johnsen B, Shekelle PG: Probiotics for the prevention and treatment of antibiotic-associated diarrhea: a systematic review and meta-analysis. JAMA 2012, 307(18):1959-69.