Gut bacteria could be evolving inside us to escape the gut: ScienceAlert


According to a new study, gut bacteria may evolve over time to live outside the gut, which could make them more dangerous, possibly leading to chronic inflammation and associated health risks to other organs in the body.

There is a lot of research explaining the positive and negative effects that gut microbes can have on our health, but scientists still don’t understand much about how these various biological mechanisms and chain reactions work.

Some health problems are attributed to what is called a “leaky gut,” where the gut is more leaky than it should be, releasing bacteria outside the digestive tract. However, there are many unanswered questions about the disease, including whether it is a symptom or a cause of inflammation issues.

“A mystery has been how potentially pathogenic bacteria can exist in healthy people for decades without apparent health consequences,” says immunobiologist Noah Palm, of Yale University.

In an attempt to solve the mystery, Palm and his colleagues introduced the potentially pathogenic bacteria Enterococcus gallinarum — a species found in about 6% of gut microbiomes in humans — in germ-free mice without gut microbes. The researchers then monitored the mice for three months.

The researchers observed the bacteria evolve into two distinct types. One was similar to the original strain, while another had small DNA mutations allowing it to live in the lining of the intestine – and to survive in the lymph nodes and liver after escaping the intestine.

More worryingly, the mutated bacteria can apparently remain hidden in organs and escape the attention of the immune system. In experiments with mice, the presence of mutant microbes could lead to inflammatory responses, including those linked to autoimmune diseases (which in humans include type 1 diabetes and multiple sclerosis).

“We think this evolutionary process starts over in each new host due to the preferential transmission of non-pathogenic strains between individuals,” says Palm.

In other words, in a human host, a niche can open up in the intestines when certain non-harmful strains travel to other people, allowing other bacteria in the gut space to evolve.

This phenomenon is known as “within-host evolution” and may explain why bacterial species living in our guts can adapt over time, scientists say. Environmental factors, including diet, have some influence on this.

The more diverse a bacterial community in the gut is, the less room a species has to grow, reducing the chances of developing unhealthy variants – those that can potentially escape. Anything that affects this diversity, such as diet, could then help explain the risk of inflammatory conditions that sometimes have “leaky gut” as a symptom, says Michael Palm, lead author of the study.

All of this means that if we can better understand this bacterial evolution, we may be able to develop and introduce preventative therapies for these health conditions – perhaps targeting specific microbes before they can escape. .

“These bacteria are essentially pre-adapted to exist in organs outside of the gut,” says Palm.

The research has been published in Nature.


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