Why Some Gut Microbes Only Make You Sick After Decades

Gut microbes as a health hazard

How potentially pathogenic bacteria can be present in humans as part of the gut flora for decades without adversely affecting health has long been a medical mystery. The latest research results now show that gut bacteria can evolve over time and become more pathogenic.

In a new study, internationally renowned Yale University experts have examined which key factors determine so-called bacterial translocation, through which gut bacteria can overcome the gut barrier. The results were published in the journal Nature.

Diseases caused by intestinal microbes

Intestinal microbes can promote health or endanger it by contributing to the development of certain diseases. These include, for example, autoimmune diseases, inflammatory bowel diseases, metabolic syndrome and even neuropsychiatric disorders.

Patient with chronic inflammatory response

The so-called leaky gut hypothesis is a common explanation for the negative effects of gut bacteria. This assumes that potentially harmful bacteria are able to escape from the gut. They then trigger a chronic inflammatory reaction, which can promote many different diseases.

Bacteria can cross the intestinal barrier

Gut bacteria can acquire the ability to cross the intestinal barrier and persist in organs outside the gut, causing chronic inflammation and related diseases, according to study author Dr. Noah Palm of the Yale University in a press release.

"However, a mystery is how potentially pathogenic bacteria can exist in healthy people for decades without any obvious health consequences," the study author continued.

Microbes divided into two populations

The team analyzed the genetics and behavior of a species of potentially pathogenic bacteria. These were introduced into germ-free mice without their own gut microbes. It turned out that the microbes gradually split into two different populations.

Mutation allows survival outside the gut

One of these populations behaved similarly to the original strain. The other populations developed tiny DNA mutations that allowed bacteria to survive in the intestinal lining.

Additionally, the bacteria were also able to survive in the lymph nodes and liver after leaving the gut, the researchers said.

Protection against the immune system

Common pathogens are quickly eliminated by the immune system. On the other hand, the small colonies of bacteria that have migrated remain hidden in the organs, allowing them to evade the immune system, at least temporarily.

Experts have noted that the presence of these bacteria can trigger inflammatory pathologies such as autoimmune diseases. This phenomenon could at least partially explain why some people carrying potentially pathogenic bacteria do not get sick and why the risk of disease increases with age, according to the researchers.

The ability of gut bacteria to become more pathogenic is enabled by a phenomenon called evolution within the host, according to the team. This explains why the individual types of bacteria present in the human gut can adapt and grow over the course of life.

Experts conclude that environmental factors influencing the rate and course of evolution also have important implications for the development of disease through the microbiota.

A healthy diet leads to a variety of bacteria in the gut

The researchers explain that people who eat mostly healthy diets develop more diverse bacterial communities in the gut, which means many different microbes have to compete for space and resources. This limits the population size of each individual species.

Limiting the population means the risk of developing potentially unhealthy variants, which can escape from the gut, is reduced. In contrast, more niches in the gut can open up in less diverse bacterial communities. This increases the likelihood of harmful bacterial variants developing, says Dr. Palmier.

“These bacteria are essentially primed to exist in organs outside of the gut. We believe this evolutionary process starts over with each new host, since non-pathogenic strains preferentially pass from person to person,” adds the doctor.

Development of new therapies in perspective

Better understanding of how evolution within the host affects bacterial properties in the gut could also lead to new therapies for diseases linked to bacteria escaping the gut, the team hopes. of research. (as)

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This text corresponds to the specifications of the specialized medical literature, medical guidelines and current studies and has been verified by health professionals.


Yi Yang, Mytien Nguyen, Varnica Khetrapal, Nicole D. Sonnert, Anjelica L. Martin, et al. : Intra-host evolution of an intestinal pathobiont facilitates hepatic translocation; in: Nature (published 07/13/2022), NatureYale University: How Gut Microbes Can Evolve and Become Dangerous (published 07/13/2022), Yale University

Important note:
This article contains general advice only and should not be used for self-diagnosis or treatment. It cannot substitute a visit to the doctor.