The role of the microbiome

What is the microbiota?

The intestinal microbiota is a complex ecosystem of bacteria, fungi, viruses and archaea, which exist in a mutualistic relationship with the host.1 The microbiota has increasingly been recognised as having an essential role in maintaining health and its dysfunction is linked to numerous disorders.2

The particular balance of micro - organisms living on each person has been shown to be unique, no two individuals have exactly the same microbiota. Maintaining a diverse yet individual balance of different species is essential for the healthy functioning of both the human host and the microbiota.3

Chronic imbalances in the microbiota can result in dysbiosis, which is associated with repeated diarrhea, nutritional imbalances, and a number of autoimmune disorders characterised by excessive inflammation, including Crohn’s disease, ulcerative colitis and irritable bowel syndrome (IBS).2,4-8 Dysbiosis is also associated with a variety of illnesses via the gut - brain axis, including anxiety and depression.9

The microbiota provides protection, immune stimulation and nutrition

Although a healthy, diverse and balanced microbiota has many physiological functions, its key roles include maintaining epithelial barrier integrity, protecting against pathogen adhesion, providing immune system modulation, and synthesizing essential vitamins and nutrients.1,3,6,10

Microbiome fonctions for the host

  • Protection

    The microbiota is the body's first line of defence against pathogenic bacterial colonisation. The physical presence of the microbiota lining the intestinal epithelium creates a protective barrier. The intestinal microbiota also produces anti - bacterial substances, which help to minimise uncontrolled growth of invasive bacteria.1,6

  • Immune stimulation

    The microbiota helps to stimulate and develop the immune system. This modulation of the immune system is thought to ensure an appropriate immune reaction to gut antigens without causing excessive or chronic intestinal inflammation. 1,10

  • Nutrition

    ln addition to supplementation of amino acids, the microbiota is able to produce essential nutrients, such as certain B vitamins and vitamin K, which cannot be synthesized by the human body.6

The microbiota is now recognized as having a profound effect on health and disease and is thought to affect virtually all aspects of human health.9 Research is accelerating in the understanding of how a healthy and diverse microbiota can ensure good health for the body as a whole, providing protection against pathogens and stimulating the immune system.2,3,6

Causes of dysbiosis

Dysbiosis is defined as a disturbance or imbalance in a biological system, for example, changes in the types and numbers of bacteria in the gut which may lead to developing different diseases.2 A major cause of intestinal dysbiosis is the taking of antibiotics. Antibiotics are often associated with the subsequent proliferation of certain species, such as Clostridium difficile, which may be life - threatening. Other factors which may contribute to dysbiosis include dietary changes, excessive alcohol or tobacco consumption, stress, disease and infections.1,3,6 Acute bacterial or viral gastroenteritis and their associated diarrhea can change the composition of the intestinal microbiota, compromising the protective microbial barrier, and resulting in worsening diarrhea.11,12

What are the consequences of dysbiosis?

Acute dysbiosis is an immediate cause of digestive troubles and may be a contributing factor to certain chronic disorders, most notably IBS. Although in most cases the root cause of the IBS is unknown, in 5% to 32% of cases IBS follows a bout of acute gastroenteritis.13 If the microbiota remains chronically unbalanced it may be associated with excessive and sustained inflammation of the intestine, which is characteristic of Crohn’s disease and ulcerative colitis.

Rebalancing the microbiota with a suitable diet and by taking ‘biotics’ to restore the natural microbial balance to the intestine are thus essential first steps and helping to treat and prevent longer - term and serious gastrointestinal diseases.3Biotics’ have the dual effect of stimulating the regrowth of the microbiota and substituting for it; thus potentially restoring the protection and immune - stimulation offered by a healthy microbiota.14,15

  1. Shin A, Preidis GA, Shulman R, Kashyap PC. The gut microbiome in adult and pediatric functional gastrointestinal disorders. Clin Gastroenterol Hepatol 2019;17:256-74.
  2. Marchesi JR, Adams DH, Fava F, et al. The gut microbiota and host health: a new clinical frontier. Gut 2016;65:330-9.
  3. Valdes AM, Walter J, Segal E, Spector TD. Role of the gut microbiota in nutrition and health. BMJ 2018;361:k2179.
  4. Lebba V, Totino V, Gagliardi A, et al. Eubiosis and dysbiosis: the two sides of the microbiota. New Microbiol 2016;39:1-12.
  5. Shi N, Li N, Duan X, Niu H. Interaction between the gut microbiome and mucosal immune system. Mil Med Res 2017;4:14.
  6. Thursby E, Juge N. Introduction to the human gut microbiota. Biochem J 2017;474:1823-36.
  7. Gorbach SL. Microbiology of the gastrointestinal tract. In: Baron S, ed. Medical Microbiology. Galveston (TX): University of Texas Medical Branch at Galveston; 1996.
  8. Morowitz MJ, Carlisle EM, Alverdy JC. Contributions of intestinal bacteria to nutrition and metabolism in the critically ill. Surg Clin North Am 2011;91:771-85, viii.
  9. Mohajeri MH, Brummer RJM, Rastall RA, et al. The role of the microbiome for human health: from basic science to clinical applications. Eur J Nutr 2018;57:1-14.
  10. Lin L, Zhang J. Role of intestinal microbiota and metabolites on gut homeostasis and human diseases. BMC Immunol 2017;18:2.
  11. Ma C, Wu X, Nawaz M, et al. Molecular characterization of fecal microbiota in patients with viral diarrhea. Curr Microbiol 2011;63:259-66.
  12. Pop M, Walker AW, Paulson J, et al. Diarrhea in young children from low-income countries leads to large-scale alterations in intestinal microbiota composition. Genome Biol 2014;15:R76.
  13. Thabane M, Marshall JK. Post-infectious irritable bowel syndrome. World J Gastroenterol 2009;15:3591-6.
  14. Patterson E, Cryan JF, Fitzgerald GF, Ross RP, Dinan TG, Stanton C. Gut microbiota, the pharmabiotics they produce and host health. Proc Nutr Soc 2014;73:477-89.
  15. Sánchez B, Delgado S, Blanco-Míguez A, Lourenço A, Gueimonde M, Margolles A. Probiotics, gut microbiota, and their influence on host health and disease. Mol Nutr Food Res 2017;61.

Diarrhea, a multifactorial disease

Acute diarrhea is defined as the abrupt onset of three or more loose stools per day with increased water content, volume, or frequency and which lasts no longer than 14 days…

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