what are the links with diseases?

We are on minefield. Every day, a new hypothesis flourishes on the microbiota and its role in this or that pathology. This gives rise to rantings shouting that it is necessary to do this, to consume this, to take such food supplements, often on the basis of very little or even nonexistent evidence.

On the other hand, that does not mean that the microbiota question and the links it has with the development of certain pathologies have not been studied. Quite the contrary. This is a rapidly expanding field, the mechanisms of which are beginning to be better understood, as attested a recent article published in the journal Public Library Of Science Pathogens ((PLOS Pathogens). But as usual when we talk about science, we must be careful, put our hopes aside and embrace uncertainty at best. This is to understand the complexity of these close ties. Let's see together what science teaches us about real connections or the study uniting microbiota and diseases.

A little history

The hypothesis of a link between our ecosystem intestinal and our health dates back to the 80s: that of the XIX^e century! This is Theodor Escherich, pediatrician and bacteriologist, who formulates it in an article published in 1885, entitled " The bacteria intestinal tracts of newborns and breastfed infants ”. This doctor is far from being anyone. To his credit in particular, the discovery of a bacterium that we now know well: Escherichia coli.

During the XX^e century, our understanding has continued to refine regarding what some now regard as an organ in its own right. Indeed, we discovered that the microbiota played a role in nutrient metabolism, protection against certain pathogens, immune system education and production of various and varied metabolites of fundamental utility for our organism.

Although the gut microbiota is generally described as being composed of microorganisms not harmful or beneficial, it is now accepted that two cash individual or multiple community members acting in synergy may have effects pathogens, which are often more subtle than those of conventional pathogens. Indeed, the presence of common intestinal microorganisms with discrete virulence factors (for example, enterotoxins and genotoxins) is manifested in diseases such as colorectal cancer or inflammatory bowel disease. This over long periods, sometimes because of some history genetic of the'host. All of these new mechanisms obscure our classic definition of the pathogen.

Since the 2000s, research has greatly accelerated, in particular thanks to the revolution “ omic " which designates high screening techniques debit. For the microbiota, it is essentially the metagenomics which can sequence thousands of bacteria at once, and metabolomics, which can screen hundreds of molecules present in the plasma, fabrics, etc.

Also, it has been shown that the microbiota is very sensitive to environmental factors such as the use of antibiotics, geography, immigration and of course, dietary changes, including deprivation of fiber. Emerging studies, often extending from observations based on " omic Provide a causal and cellular understanding of the relationships that link host responses to changes in the microbiota and its metabolism. Let's see this in a little more detail.

The microbiota, this metabolite plant

The microbiota is a complex environment. We now know that it produces metabolites which influence all the other systems of the organism, which is why it is considered as an organ in its own right as specified above in the article. Indeed, the microbiota and especially its production of metabolites intervene at the level of brain, lungs, heart, liver, Small intestine and colon. Just that !

For the brain, the metabolites produced (or not produced) by the microbiota would have an influence in autism, Parkinson's disease, the Depression and the multiple sclerosis. Concerning the lungs, studies suggest an implication in diseases such as asthma or respiratory allergies. At the level of the cardiovascular system, these would play a role in the whole cardiovascular disease. About the colon and the small intestine, an impact on celiac disease, the irritable bowel syndrome and colorectal cancer appear very likely. Finally, our microbiota and its metabolites are involved in metabolism of various drugs and could play a role in the appearance nonalcoholic fatty liver disease.

Even if these studies point to interesting lines of research, not to say exciting for future applications However, this knowledge must be taken with the necessary hindsight. This article is a review that reports on what is known about microbial metabolites, that is, all the molecules produced by the microbiota. We know that some of these molecules have effects on the organism: Fatty acids short chain, secondary bile acids or lesser known molecules like imidazole propionate. In addition, some molecules are "beneficial" while others play a rather deleterious role. The question for the next few years is how we can modulate this microbial balance to tip the balance on the beneficial side.

Towards an upheaval in medicine?

As we have seen, the microbiota and the metabolites that it produces would enormously influence the state of health of the host to the point of protecting it from certain diseases or, on the contrary, participating in their occurrence or progression. This is the challenge of clinical research for the next few years. With the basic research carried out for almost three decades now on the microbiota, one could imagine treatments which tend to favor certain pathways of microbial synthesis to increase the production of such or such metabolites in order to prevent diseases in the long term or in cure some.

However as always: be careful. Although progress has been phenomenal in this area of ​​research, the paradigm shift at the medical level is not likely to be immediate. In terms of discoveries, we have gradually moved from a simple paradigm (changing the composition of the microbiota, but without really understanding what it meant) to understanding the mechanisms. Such a bacterium produces such a molecule by such a synthetic route. The idea is to stimulate this synthetic route or to bring in said bacteria. For the moment we are still far from it. But research is progressing.