Our Head of Research & Development Dr Miguel Toribio-Mateas has been putting together a glossary of terms that you’re likely to come across when reading about the gut microbiome. The idea is to translate and distil complex science into bite-size posts, written in plain English, because knowledge is power! Understanding the finer points about how your microbiome works is like having the user’s manual to your own system, right in your hands. So let’s get started…
For our very first post in this series, we’re focusing on “commensal bacteria”.
What are commensal bacteria?
The human body consists of about 100 trillion cells and carries about ten times as many microorganisms in the gut. 1O’Hara AM, Shanahan F. The gut flora as a forgotten organ. EMBO Rep. 2006 Jul;7(7):688-93. doi: 10.1038/sj.embor.7400731. There are commensal bacteria in a range of tissues around the body, not just in the gut but in the mucous membranes of the mouth, the airways, the genitals and the eyes, as well as on the skin. But what does “commensal” mean? Commensal is a term used in scientific literature to refer to the communities of bacteria that live among other microbes, often creating mutually beneficial arrangements with other microbes, starting at birth and lasting a lifetime.2Neu J, Rushing J. Cesarean versus vaginal delivery: long-term infant outcomes and the hygiene hypothesis. Clin Perinatol. 2011 Jun;38(2):321-31. doi: 10.1016/j.clp.2011.03.008. As humans, we have intimate symbiotic relationships with commensal bacteria too. We contribute to their balance, and they do the same for us, helping us regulate our immune function. Loss of microbial balance known as dysbiosis is now well documented as a factor leading to disease.3Hou K, Wu ZX, Chen XY, Wang JQ, Zhang D, Xiao C, Zhu D, Koya JB, Wei L, Li J, Chen ZS. Microbiota in health and diseases. Signal Transduct Target Ther. 2022 Apr 23;7(1):135. doi: 10.1038/s41392-022-00974-4.
What are examples of commensal bacteria?
In the adult gastrointestinal tract Bacteroidetes and Firmicutes make up about 90% of the bacteria. Other important high level groups of bacteria – referred to as “phyla” in biology – are Actinobacteria, namely Bifidobacterium, Proteobacteria, and Verrucomicrobia, namely Akkermansia muciniphila.4Sekirov I, Russell SL, Antunes LC, Finlay BB. Gut microbiota in health and disease. Physiol Rev. 2010 Jul;90(3):859-904. doi: 10.1152/physrev.00045.2009.5Eckburg PB, Bik EM, Bernstein CN, Purdom E, Dethlefsen L, Sargent M, Gill SR, Nelson KE, Relman DA. Diversity of the human intestinal microbial flora. Science. 2005 Jun 10;308(5728):1635-8. doi: 10.1126/science.1110591.
What do commensal bacteria do?
Commensal bacteria – also referred to as “commensal microbiota” – play a key role in the extraction of nutrients from the foods we eat and get fed in the process. This mutually beneficial arrangement helps them get established in different locations along the gastrointestinal tract, from the mouth to the anus. The colonisation of these different locations leads to the development of immune cells with specific functions with which commensals continue to interact throughout our lifetime, helping us create a protective mechanism against disease-carrying microorganisms.6Ma N, Guo P, Zhang J, He T, Kim SW, Zhang G, Ma X. Nutrients Mediate Intestinal Bacteria-Mucosal Immune Crosstalk. Front Immunol. 2018 Jan 24;9:5. doi: 10.3389/fimmu.2018.00005.
There are well documented links between different commensal bacteria and the development of a range of conditions, from ulcerative colitis to Parkinson’s disease.7Sorini C, Cardoso RF, Gagliani N, Villablanca EJ. Commensal Bacteria-Specific CD4+ T Cell Responses in Health and Disease. Front Immunol. 2018 Nov 20;9:2667. doi: 10.3389/fimmu.2018.02667. These will be highlighted in more detail in upcoming posts.
How can you promote your commensal bacterial balance?
This is a bit like asking “how can we promote the health of a forest?” Both the gut and a forest are complex ecosystems with a multitude of living organisms that can contribute to its health. The key to the answer is balance, or “homeostasis” in scientist-speak.
Several factors are responsible for the composition and the function of commensal bacteria. These include age, diet, physical activity / exercise, stress, exposure to drugs/chemicals.8Conlon MA, Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients. 2014 Dec 24;7(1):17-44. doi: 10.3390/nu7010017.9Krishnan S, Alden N, Lee K. Pathways and functions of gut microbiota metabolism impacting host physiology. Curr Opin Biotechnol. 2015 Dec;36:137-45. doi: 10.1016/j.copbio.2015.08.015.
You can make conscious changes to your lifestyle that have a positive impact on the overall balance of your gut commensals. Science tells us that eating a range of colourful plant foods as a source of nutrients known as polyphenols is one of the most likely impactful things you can do.10Kumar Singh A, Cabral C, Kumar R, Ganguly R, Kumar Rana H, Gupta A, Rosaria Lauro M, Carbone C, Reis F, Pandey AK. Beneficial Effects of Dietary Polyphenols on Gut Microbiota and Strategies to Improve Delivery Efficiency. Nutrients. 2019 Sep 13;11(9):2216. doi: 10.3390/nu11092216.11Ribeiro FM, Lopes G, da Cunha Nascimento D, Pires L, Mulder AP, Franco OL, Petriz B. An overview of the level of dietary support in the gut microbiota at different stages of life: A systematic review. Clin Nutr ESPEN. 2021 Apr;42:41-52. doi: 10.1016/j.clnesp.2021.01.024.
Including a range of fermented foods in your diet will also help.12Leeuwendaal NK, Stanton C, O’Toole PW, Beresford TP. Fermented Foods, Health and the Gut Microbiome. Nutrients. 2022 Apr 6;14(7):1527. doi: 10.3390/nu14071527.13Stiemsma LT, Nakamura RE, Nguyen JG, Michels KB. Does Consumption of Fermented Foods Modify the Human Gut Microbiota? J Nutr. 2020 Jul 1;150(7):1680-1692. doi: 10.1093/jn/nxaa077.,14Wastyk HC, Fragiadakis GK, Perelman D, Dahan D, Merrill BD, Yu FB, Topf M, Gonzalez CG, Van Treuren W, Han S, Robinson JL, Elias JE, Sonnenburg ED, Gardner CD, Sonnenburg JL. Gut-microbiota-targeted diets modulate human immune status. Cell. 2021 Aug 5;184(16):4137-4153.e14. doi: 10.1016/j.cell.2021.06.019.
Kefir is particularly helpful,15Peluzio MDCG, Dias MME, Martinez JA, Milagro FI. Kefir and Intestinal Microbiota Modulation: Implications in Human Health. Front Nutr. 2021 Feb 22;8:638740. doi: 10.3389/fnut.2021.638740. and keeping active is also a good way to keep your gut commensals happy.16Aya V, Flórez A, Perez L, Ramírez JD. Association between physical activity and changes in intestinal microbiota composition: A systematic review. PLoS One. 2021 Feb 25;16(2):e0247039. doi: 10.1371/journal.pone.0247039.
Some really cool facts about commensal bacteria
It seems incredible that we are only beginning to fully understand the science of how food affects brain health via the gut-brain connection or “gut-brain axis”. We are even less acquainted with the “brain-to-gut” branch of this communication system; our thoughts affect our emotional state, and this contributes to health as well as to disease.
As an example, whenever we feel anxious, we release a myriad of natural chemicals that are part of the human stress response. These stress molecules affect not only our brain but our gut. So, by being mindful of our reactions to everyday life situation, we can bring balance to this all important communication system17Herselman MF, Bailey S, Bobrovskaya L. The Effects of Stress and Diet on the “Brain-Gut” and “Gut-Brain” Pathways in Animal Models of Stress and Depression. Int J Mol Sci. 2022 Feb 11;23(4):2013. doi: 10.3390/ijms23042013.
Where can you find commensals in our microbiome test?
Our microbiome test focuses on commensal bacteria. This means that literally every one of the bacteria you find in our test is a member of your gut’s commensal bacteria community.
To understand more about the “gut-brain axis” read the post “What’s the quickest way to boost your mental health.”
References
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