Mireia Vallès-Colomer, microbiologist: “Without bacteria, our life is not possible” | Health & Wellness

2023-07-12 05:20:00

Mireia Vallès-Colomer, microbiologist and postdoctoral researcher at the University of Trento (Italy).Fabio Colombi

The microbiome is on everyone’s lips. Literally. There is, in fact, a world of microorganisms that populate the oral cavity, the intestine, the vagina… and that fulfill essential functions for the organism. The scientific community knows that millions of bacteria, viruses, fungi or yeasts coexist in harmony within the body and work for life, but they do not know exactly how they do it, or to what extent their influence reaches. Much remains to be discovered, admits Mireia Vallès Colomer (33 years old, Vic, Barcelona), microbiologist and postdoctoral researcher at the Computational Metagenomics Laboratory of the University of Trento (Italy) and expert in the study of the impact of the intestinal microbiome on health: “It has gone from completely ignoring it to being the solution to everything. I believe that the truth is in the middle: it can help us with many diseases, but by itself it will not be the solution”, the researcher advances in a videoconference interview with EL PAÍS, a few days before participating in a symposium on the microbiome. organized by IrsiCaixa in Barcelona.

Vallès Colomer, who has a Master’s in Molecular Sciences and a PhD in Biomedicine, has seen the lightning rise of the microbiome as an object of study in recent years, how the eyes of the scientific community have settled on this ecosystem of microbes to seek answers to dozens of diseases. She has done it too: the researcher opened a thread of connection between mental health problems and the intestinal microbiome by discovering different bacterial compositions between people with depression and healthy people. Vallès Colomer also published a study last year that revealed that bacteria are transmitted between people through social interactions: two cohabitants share 12% of the strains in their intestines and up to 32% in their mouths.

Ask. The study of the microbiome is everywhere, mentioned in scientific articles of all kinds. But, usually conditionally: it could have a role in health and disease. What do they really know about that ecosystem of microorganisms that populates the intestine?

Answer. In a decade or so, the field has grown tremendously and we have learned a lot. Our big problem is that we always have associations. In other words, they are descriptive studies: we see that if we compare people with a disease and other healthy ones, there are these differences, but what is difficult is establishing causality. Alterations in the microbiome could be a cause or a consequence of the disease. Or not at all, it could be that people with this disease eat differently, and that their microbiome would change because of those differences in diet.

Q. How does the microbiome mediate health and disease?

R. We know, and this is the clearest evidence, that without bacteria our life is not possible. Inside our bodies, they help us with digestion: fibers are super important for health, but we cannot digest them, they are digested by the bacteria that we have in our intestines. They also produce vitamins, many essential micronutrients and keep our immune system controlled, train it and also, being there, protect us from pathogens.

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Q. What happens when the disease appears? Experts speak of a dysbiosis, of an imbalance in that ecosystem, but what does that mean?

A. Dysbiosis is an alteration of the microbiome from the normal composition, although the normal composition is also a very big definition because two healthy people have different compositions. Many times what happens is that there is a loop: you have a microbiome with many diseases, less diverse, less resilient to external stimuli, and this already contains less inflammation: more inflammation is created, by the immune system or, in many cases, because a pathogen arrives. And all this changes the composition of the microbiome and causes pathogenic species, which are often already there, but at super-low levels and do nothing to us, to have the conditions that most favor their survival.

Q. In 2019, you participated in a study that identified two genera of bacteria, Coprococcus and Dialister, that were in short supply in people with depression. What does this mean?

A. This is an association: we see that these people have lower levels than the rest of the population. We are going to see what are the properties of these bacteria and we find that many of them are producers of butyrate, which is the main source of energy for colonocytes, the cells of the intestine, and also lowers inflammation levels. Surely what is happening is that these people have a more pro-inflammatory microbiome. Within a genus of bacteria there may be strains that are very different from each other and that is why we are now developing more precise methods, because perhaps the problem is not a whole genus of bacteria, but only some strains.

Q. How does the gut-brain axis work? How do they dialogue?

R. It is important and we are seeing several mechanisms that are related. One part is through nerve pathways, that is, the vagus nerve: neurons that occur in the intestine and reach the brain. Another mechanism is inflammation, which is also related to cortisol, which is the stress hormone. And the third is the direct production of many neurotransmitters in the gut: a very large portion of the serotonin, dopamine, and gaba in our bodies is produced in the gut, not the brain, and there is a portion that can travel into the general circulation and from there to the brain. But there are molecules that do not and even so, they can have a function.

Q. Was it focusing in the wrong place by historically focusing attention on the brain to treat mental health problems? Should one look a little further down, in the intestine?

A. I wouldn’t say it’s wrong or that you just have to lower your eyes, but zoom in and study the whole body, not just focus on the brain. We know that the main problem may be there, but it is not only there. And that is related to the fact that the treatments for depression do not work well and perhaps what we could do is develop therapies to improve the composition of the microbiome. In the end, what we need is a more global medicine.

Q. How much does the microbiome influence mental health? What is the level of intensity of this relationship and what pathologies does it affect?

R. The intensity is very clear and, in reality, it does not need to be at a scientific level. You know that all people, when they have moments of anxiety, also have gastrointestinal problems. And when you eat worse for whatever reason, your stress levels skyrocket. What we are trying to understand is the mechanism.

Q. Do the hypotheses that you raise in depression extend to other mental health or neurological problems, such as autism?

R. In the specific case of autism, what we see is that there are many published articles, but with different results. And there’s a new paper from last year on autism that what it does is take a better look at children’s eating patterns and they see that many of these disturbances can actually be explained by eating behaviors. So perhaps the differences we see in the microbiome are not just from disease, but from children eating differently. In other diseases, such as Parkinson’s or Alzheimer’s, there are clear patterns. Almost for every disease we can think of, you come across an article that shows you that there are differences in the microbiome; but the important part is to see if they are really signs of the disease, or of the treatment, or if they are eating patterns or something else.

Q. What is meant by a healthy microbiome if each healthy person has a different microbiome?

R. The high diversity. It may be that the bacteria that are there are different between two people, but the two people are going to have a high diversity of microbes.

Q. In one of your studies, you revealed that social interactions somehow shape our microbiome. Does that mean that everything sticks, even our bacteria?

A. Yes, to a certain extent, yes. When the baby is born, it is born almost sterile and receives all its bacteria from its mother. But what we see is that babies lack many of the typical adult bacteria, meaning that we have to acquire them sooner or later. The new part of this year’s article is that in adults there is also a lot of sharing and this is not a bad thing. Do I have to be more hygienic? Not for us. A more diverse microbiome is a positive thing. More interaction with more people is one thing that will enrich your microbiome.

Q. How is this transfer of microbes done? Does living with one person have the same influence as going to a party with 200?

A. For the gut microbiome it is important that the interaction is prolonged. If you run into one person in the supermarket, or many in the disco, you may not be going to exchange anything. Quality social interactions are needed.

We know that stool transplantation is an emergency solution, not a definitive one”

Q. If we enrich ourselves with the microorganisms of others, can we also spread dysbiosis and, therefore, non-communicable diseases can become so?

R. This is a hypothesis that we consider: it could be that diseases non-transmissible become transmissible through microbiome. But this is a hypothesis. We did the first study in healthy people and we saw that there is a lot of transmission. We think that, since there is diversity in healthy people, these bacteria will win over a dysbiotic community with fewer bacteria and less resistance to colonization. We do not think that living with people with dysbiosis is a problem, but the other way around: it will be positive. But this is all a hypothesis because we do not yet have studies of microbial transmission in people with diseases.

Q. The microbiome is studied a lot, but there are no great effective treatments. It seems that it is not easy to manipulate or change it.

A. No, it is not easy. We believe that we have to follow a personalized medicine perspective: we cannot give any probiotic for any alteration of the microbiome. And on the market, almost all formulations are very similar. For probiotics, the solution is going to be something much more personalized and complex. And stool transplantation is approved for Clostridioides difficile infection, but we don’t think this is the ultimate solution either: if you find a formulation of bacteria that works, it’s going to be a lot more accurate than giving stool from a healthy person. Stool transplantation is being studied for more diseases, there are tests for depression, but we are still trying to understand what makes a good donor, there are still many questions and we know that it is an emergency solution, not a definitive one.

Q. What should the population know to take care of their microbiome?

A. The easiest part is clearly eating, eating healthier: there are many fads here, but, in the end, eating more fiber and less processed foods is going to help us a lot, along with an active lifestyle. And relating to more people is also associated with a higher quality of life, greater mental health.

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