An Extraordinary Balance

Microbial Composition Along the GI Tract

The composition of the gut microbiome is not homogenous and differs by location along the GI tract.10,13 Differences in diversity and absolute counts of bacterial species are dictated by local biochemical factors, including pH and oxygen levels.5,10

In the stomach and upper small intestine, acidic pH and high oxygen levels limit bacterial abundance and type, favoring the growth of aerobes.10

In the colon, a more alkaline pH, slower motility, and lower oxygen levels enable greater diversity and abundance and promote the growth of anaerobes.10

Microbial Imbalance and Chronic Disease

Although composition varies widely, a healthy gut microbiome is generally described as abundant, diverse, and resistant to stress-related change.3,5 When altered, microbial composition can favor the development of chronic diseases, such as3,5,7,14,21,22:

  • Obesity
  • Inflammatory bowel disease
  • Irritable bowel syndrome
  • Type 2 diabetes mellitus
  • Autism
  • Psoriasis

The gut microbiome may also affect mental health via the gut-brain axis.14,21,23 Evidence suggests that signals from the CNS can alter the gut microbiota and, in return, these alterations can affect brain function.23 Changes in gut microbial composition have been associated with psychiatric disorders, such as major depressive disorder; however, studies cannot conclude whether dysbiosis was a cause or consequence of these disorders.14,15,21,23 In addition, this connection has been assessed primarily in animal models and has not been validated in humans.14,21,23

microbial composition in different areas of GI tract, including esophagus, stomach, duodenum. Jejunum, ileum, colon

Adapted, with permission, from: Gorkiewicz G, Moschen A. Gut microbiome: a new player in gastrointestinal disease. Virchows Arch. 2018;472(1):159-172.

 
 
CAUSES AND CONSEQUENCES OF GUT DYSBIOSIS >>
GI = gastrointestinal.
pH = power of hydrogen.
CNS = central nervous system.
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References

  1. Lloyd-Price J, Abu-Ali G, Huttenhower C. The healthy human microbiome. Genome Med. 2016;8(1):51
  2. Ursell LK, Metcalf JL, Parfrey LW, Knight R. Defining the human microbiome. Nutr Rev. 2012;70(suppl 1):S38-S44.
  3. Sidhu M, van der Poorten D. The gut microbiome. Aust Fam Physician. 2017;46(4):206-211.
  4. Ringel Y. The gut microbiome in irritable bowel syndrome and other functional bowel disorders. Gastroenterol Clin North Am. 2017;46(1):91-101.
  5. Quigley EM. Gut bacteria in health and disease. Gastroenterol Hepatol (N Y). 2013;9(9):560-569.
  6. Raskov H, Burcharth J, Pommergaard HC, Rosenberg J. Irritable bowel syndrome, the microbiota and the gut-brain axis. Gut Microbes. 2016;7(5):365-383.
  7. Passos MDCF, Moraes-Filho JP. Intestinal microbiota in digestive diseases. Arq Gastroenterol. 2017;54(3):255-262.
  8. Distrutti E, Monaldi L, Ricci P, Fiorucci S. Gut microbiota role in irritable bowel syndrome: new therapeutic strategies. World J Gastroenterol. 2016;22(7):2219-2241.
  9. Flint HJ, Scott KP, Louis P, Duncan SH. The role of the gut microbiota in nutrition and health. Nat Rev Gastroenterol Hepatol. 2012;9(10):577-589.
  10. Gorkiewicz G. Moschen A. Gut microbiome: a new player in gastrointestinal disease. Virchows Arch. 2018;472:159-172.
  11. Dong TS, Gupta A. Influence of early life, diet, and the environment on the microbiome. Clin Gastroenterol Hepatol. 2019;17(2):231-242.
  12. Cresci GA, Bawden E. Gut microbiome: what we do and don’t know. Nutr Clin Pract. 2015;30(6):734-746.
  13. Shin A, Preidis GA, Shulman R, Kashyap PC. The gut microbiome in adult and pediatric functional gastrointestinal disorders. Clin Gastroenterol Hepatol. 2019;17(2):256-274.
  14. Carding S, Verbeke K, Vipond DT, Corfe BM, Owen LJ. Dysbiosis of the gut microbiota in disease. Microb Ecol Health Dis. 2015;26:26191.
  15. Wang B, Yao M, Lv L, Ling Z, Li L. The human microbiota in health and disease. Engineering. 2017;3:71-82.
  16. Jandhyala SM, Talukdar R, Subramanyam C, Vuyyuru H, Sasikala M, Reddy DN. Role of the normal gut microbiota. World J Gastroenterol. 2015;21(29):8787-8803.
  17. Cani PD. Human gut microbiome: hopes, threats and promises. Gut. 2018;67(9):1716-1725.
  18. Ghoshal UC, Shukla R, Ghoshal U, Gwee KA, Ng SC, Quigley EM. The gut microbiota and irritable bowel syndrome: friend or foe? Int J Inflam. 2012;2012:151085.
  19. Kennedy PJ, Cryan JF, Dinan TG, Clarke G. Irritable bowel syndrome: a microbiome-gut-brain axis disorder? World J Gastroenterol. 2014;20(39):14105-14125.
  20. Tillisch K. The effects of gut microbiota on CNS functions in humans. Gut Microbes. 2014;5(3):404-410.
  21. Brett BE, de Weerth C. The microbiota-gut-brain axis: a promising avenue to foster healthy development outcomes. [published online ahead of print January 14, 2019]. Dev Psychobiol. doi:10.1002/dev.21824
  22. Forbes JD, Van Domselaar G, Bernstein CN. The gut microbiota in immune-mediated inflammatory diseases. Front Microbiol. 2016; 7:1081.
  23. Lee KN, Lee OY. Intestinal microbiota in pathophysiology and management of irritable bowel syndrome. World J Gastroenterol. 2014;20(27):8886-8897.
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