Wednesday, October 27, 2021

Some antibiotics can kill “helpful” intestinal bacteria, study results

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October 13 (News) – Tetracyclines and macrolides, two commonly used classes of antibiotics, stop beneficial gut bacteria from growing and ultimately kill them, according to a study published Wednesday by Nature.

In an analysis of the effects of 144 commonly prescribed antibiotics on the gut microbiome, the collection of helpful bacteria that aid digestion and boost immunity, about half of the strains tested did not survive treatment with these antibiotics, the data showed.

While these drugs are critical in treating bacterial infections and saving millions of lives, they also weaken one of the body’s first lines of defense against pathogens and undermine the diverse beneficial effects of the microbiota on health, the researchers said.

Common side effects of what researchers call “collateral damage” from antibiotics are gastrointestinal problems and recurrent Clostridioides difficile or C. diff infections.

The drugs also contribute to long-term health problems such as the development of allergic, metabolic, immunological or inflammatory diseases, according to the researchers.

“Many antibiotics inhibit the growth of various pathogenic bacteria,” said study co-author Lisa Maier in a press release.

“This broad spectrum of activity is useful in the treatment of infections, but it increases the risk that the microbes in our intestines will also be attacked,” says Maier, a researcher at the University of Tübingen.

The gut microbiome is made up of many different microbial species and viruses that enable the body to use nutrients more efficiently and prevent harmful bacteria from settling in our gut, according to the Harvard TH Chan School of Public Health.

However, when bacterial infection is treated with antibiotics, there is a risk of harming the gut microbiome, leading to an imbalance in our microbiota composition commonly known as dysbiosis, Maier and her colleagues said.

Diarrhea is a common short-term effect of dysbiosis, while allergic conditions such as asthma or food allergies and obesity are possible long-term effects.

It has long been known that antibiotics are also effective against gut microbes, but their effects on the wide variety of microbes in the gut remain unclear, according to the researchers.

For this study, Maier and her colleagues examined how 144 frequently prescribed antibiotics influenced the growth and survival of up to 27 bacterial strains in the gut microbiome.

For more than 800 antibiotic strain combinations, the researchers determined the concentrations at which a certain antibiotic affects these bacterial strains.

Tetracyclines and macrolides selectively killed certain gut microbes, meaning their use could result in these microbes being lost from the gut microbiota much faster than microbes that are only growth stunted, the researchers said.

This could explain the profound changes in microbiota experienced by some patients treated with these antibiotics, they said.

“We did not expect this effect with tetracyclines and macrolides,” said study co-author Camille Goemans in a press release.

“Doxycycline, erythromycin and azithromycin, three commonly used antibiotics, have killed several microbial species found in the intestine,” says Goemans, postdoc at the University of Tübingen.

There might be a way to lessen the harm, however, as the researchers combined the antibiotics erythromycin or doxycycline with a set of nearly 1,200 drugs to identify drugs that would protect two common types of gut bacteria from these antibiotics.

In doing so, they identified several non-antibiotic drugs that could save these gut microbes and other related species, the researchers said.

And the combination of an antibiotic with a protective second drug did not affect the effectiveness of the former against harmful bacteria.

“Our approach of combining antibiotics with a protective antidote could open up new opportunities to reduce the harmful side effects of antibiotics on our intestinal microbiome,” said Maier.

“No single antidote will be able to protect all bacteria in our intestines, especially since they vary so much from person to person, but this concept opens the door for the development of new personalized strategies to keep our intestinal microbes healthy,” said she.

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