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'Good' Bacteria in Probiotics Could Evolve in the Gut to Do Harm, Experiment Suggests



Probiotics are sold to us as 'good' bacteria that help balance out 'bad' varieties of microbes camping out in our gut. But a new experiment on the mouse has shown how our microbial allies can evolve into traitorous backstabbers that risk causing damage to our guts

"If we are going to use living things as medicines, we need to recognize that they are" "That's what you put in your body," says Gautam Dantas, patologist and biomedical engineer.

Unlike other forms of medication, living organisms literally have a life of their own. What you swallow can reproduce.

"There is no microbe out there that is immune to evolution," says Dantas.

Dantas led by a team of researchers from the University of Washington who evaluated a bacterium marketed to help fight diarrhea .

Just over 1

00 years ago, and a German physician named Alfred Nissle found some strains of Escherichia coli could be used to treat patients who were suffering from infectious diseases.

One strain in particular still stands out for his talent in the fight against acute diarrhea, especially in young children. E. coli Nissle 1917 (EcN) has been shown to be a safe and effective treatment for what can be a deadly condition

To evaluate the potential of EcN's evolution after it's swallowed, the research team used mice specially bred to be completely germ free

The test subjects were divided into four groups, each with a distinct gut microbiome. One was left completely sterile; the other three were given microbiomes reflecting various healthy and unhealthy states

Each group was dosed with EcN and then fed one of the following options – a prancing old lab mouse chow, a more natural diet friendly to myrrh, fats and sugars, and a Westernized diet that had some fiber added.

Five weeks later, the mice had their guts examined. Those happy little E. coli ? It has been found that they were not quite as friendly as they were on their way, especially in guts that had to deal with less than healthy diets.

Inside mouse guts filled with westernized foods, EcN had accumulated mutations that helped (19659003) These bacteria also adapt to become a bit sticker, giving them a competitive edge over other residents

More about, the EcN within a group of mice treated with streptomycin had evolved a low level of resistance to the antibiotic

"In a healthy, high-diversity background we did not capture a lot of adaptation, perhaps because this is the background that Nissle is used to, "says Aura Ferreiro, a biomedical engineering graduate student

" But you have to remember that quite often we would not be using probiotics in people with a healthy microbiome. "

These tricks might have been great news for the probiotic E. coli trying to make a home in their new environment, but for their host it poses a significant concern

Sticky bacterial cells that cope with stress by evolving easily to break down carbohydrates are not what we sign up for with probiotics

The results show that popular probiotics such as EcN are not the kind of friendly guests we might want in our homes, but there are opportunistic scavengers that will turn on us if we do not treat them with the right level of affection

Before we furiously flush our germ pills, there's a few things to keep in mind.

This is a mouse study. As we all know, there's a leap of anatomy between these tiny mammals and humans. It is a good first step in research that could warrant investigation, but not an immediate cause for alarm

There is also an intriguing epilogue to the study. The research team introduced a gene for degrading the amino acid phenylalanine into their strain of E. coli and developed it into a probiotic

Some people have a condition called phenylketonuria that stops them from adequately breaking down this protein building block on their own, resulting in a build-up that can threaten brain damage. 19659003] Giving this probiotic to mice engineered with a similar condition temporarily helped them metabolize phenylalanine, lowering their levels by half.

The DNA of the engineered EcN also remained relatively stable over the week of treatment, suggesting that common probiotics might benefit from a helping hand

"We can use the principles of evolution to design a better therapist that is carefully tailored to the people who need it."

"This is an opportunity, not a problem, "says Dantas.

Probiotics clearly have a lot of potential for our health.

Cell Host & Microbe

This research was published in


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