The microbiota is the set of microbial organisms in a community, generally used in reference to an animal host. The digestive microbiota is the most common.
What we call a microbiome is the set of microorganisms living in a particular environment. The microbiome (the habitat) contains the microbiota (the species).
There are more than 10 000 microbial species in the human body. The human microbiota includes bacteria, viruses, fungi (yeasts), archaea and other microorganisms present on or in the human body:
– On the skin: the skin microbiota, which feeds on sebum and dead cells. The cutaneous microbiota would have approximately one million bacteria per square centimetre of skin. The skin bacterium Propionibacterium acnes is implicated in acne.
– In the mouth: the oral microbiota represents an important part of the human microbiota, and includes several hundred to several thousand diverse species. It is a normal part of the oral cavity and has an important function to protect against colonisation of extrinsic bacteria which could affect systemic health. On the other hand, the most common oral diseases caries, gingivitis and periodontitis are based on microorganisms
– In the respiratory tract: The lung microbiota, is the pulmonary microbial community consisting of a complex variety of microorganisms found in the lower respiratory tract particularly on the mucous layer and the epithelial surfaces. These microorganisms include bacteria, fungi, viruses and bacteriophages.
– In the genitals: the vaginal microbiota, with numerous lactobacilli promoting the acidity of the vagina.
– In the digestive tract: the gut or intestinal microbiota.
The last is the one we are interested in here. We will now describe its function and composition more precisely.
Human gut microbiota
The gut microbiota, in other words the intestinal flora, has been the subject of growing interest from researchers and doctors for the past ten years.
Current research suggests that it plays a very important role in the human body and that it regulates many physiological processes.
It could also be involved in the occurrence and evolution of various diseases, including multiple sclerosis. But the microbiota is still far from having revealed all its secrets.
The gut microbiota contains the largest bacterial community in the human body, located mainly in the small intestine and in the colon. The intestinal microbiota is formed from birth, through contact either with the vaginal flora in the event of a vaginal birth, or with microorganisms in the environment or the skin in the event of a caesarean birth.
The composition of the microbiota then evolves gradually during early life, depending on diet, but also on the environment, hygiene and any medical treatment. It stabilises for the most part around the second year of life.
Once established, the intestinal microbiota remains rather stable throughout life. However, its composition can be influenced by diet, antibiotic or other treatments, or by taking toxic substances such as alcohol or tobacco.
– The digestion. The microbiota participates in the conversion of food into nutrients and allows the assimilation of certain vitamins which would otherwise be impossible.
– The maturation of the immune system. It allows the gut immune system to learn which microorganisms are beneficial and which are pathogenic.
– Protection against pathogens. The intestinal microbiota is essential for the intestinal wall to fully play its role as a barrier against pathogens from food and the environment.
When the composition of the gut microbial diversity is altered, that is to say when there is a too high level of gut microbes or other abnormality in microbial diversity it causes intestinal dysbiosis.
Stress, taking medication, antibiotics, illnesses or infections or simply an unbalanced lifestyle with too rich a diet, too much sedentary lifestyle or even lack of sleep, can mess up our intestinal microbiota.
Consequences of microbiota disturbance
Dysbiosis can lead to disease manifestation throughout the entire human body because of the link between gut microbiota and immune system.
One of the consequences of this link can be described in the experiment report that follows: researchers from the University of Bath team have identified the potential link between the gut microbiota and the immune system. More specifically, this study identifies two classes of microbial molecules, short-chain fatty acids and secondary bile acids.
Both molecules only exist in the gut at healthy and sufficient levels when certain microbes are given the right conditions to thrive: these microbes help digest certain nutrients or foods, such as fibre and green leafy vegetables.
These would influence the production of P-glycoprotein (P-gp). P-gp, had already been identified as an immunomodulator during neuro-inflammatory responses. P-gp is expressed by astrocytes in the adult brain.
The astrocytes are glial cells of the brain and active partners of neurons, they participate directly in the modulation of neuronal activity within the synapses, and also play a role in the control of cerebral blood flow, the regeneration of nervous tissue, or the neuro-inflammation.
So, if a depletion of the bacterial flora would reduce the expression of P-gp, astrocytes are altered and it can have a direct impact on neuronal activity and cause neurodegenerative diseases such as Alzheimer.
Risk of diseases
This new understanding provides insight into how the microbiome can affect the expression of the immunomodulatory protein P-gp, the astrocytes and so the functioning of the brain.
Prof. C. Ronald Kahn and members of his laboratory recently demonstrated that the intestinal microbiota can modify the behaviour of mice by sending signals responsible for the regulation of insulin (a hormone naturally secreted by the pancreas and which enables sugar to enter the body’s cells) to the brain . To highlight this link between the brain, intestine and microbiota, the scientists evaluated the behaviour and activity of insulin in rodents whose obesity had been induced, whether or not they had received antibiotic treatment.
Taking antibiotics altered the composition of the intestinal microbiota of obese mice. These mice were made obese by means of a high-fat diet. They were subjected to this diet for the six weeks that the study lasted. During the last two weeks of the study, antibiotic treatment reduced blood sugar and insulin levels in obese mice.
After the antibiotic treatment was completed, blood glucose and insulin levels rose again. These results suggest that antibiotics could be the way to reduce blood sugar and insulin levels through changes in the gut microbiota.
Disturbance of the microbiome can induce other pathologies:
- Diabetes risk;
- Dysregulation of our immunity;
- Tendency to gain weight;
- Colon inflammation;
- Porosity of the intestinal wall;
- Risk of colon cancer;
- Excess production of ethanol by certain bad bacteria;
- Excess manufacturing indole that can destabilise the brain;
- Excess production of tmao, produced by certain bad bacteria and which will endanger the vessels of the heart and brain and weaken our immune defences.
There are some key comportment to adopt in order to support and rebuild our intestinal microbiome:
- Regularly consume fibres (prebiotics) contained in fruits and vegetables, especially legumes (lentils, beans, peas, etc.), but also whole and semi-whole grains (bread, rice, muesli, etc.).
- Consume more fermented and unpasteurized lacto-fermented foods rich in probiotics
- Avoid sugary foods; ultra processed and sweeteners
- Try to limit animal fats
- Favour good fats, especially Omega-3s, which have anti-inflammatory properties
- Prefer organic foods or foods from sustainable agriculture
Even all the relations induced by the life and interactions of these microorganisms haven’t yet been discovered, researchers still progress to better understand these mechanisms and numerous medical conclusions are already available in order to better take care of our health and to better heal diseases linked to microbiota disturbance.