Research: How common preservatives affect gut health

To keep food products fresh, food manufacturers often add preservatives. A primary purpose of these preservatives is to kill microbes that could break down and spoil the food. Common additives like sugar, salt, vinegar and alcohol have been used as preservatives for centuries, but modern-day food labels can include unfamiliar ingredients such as sodium benzoate, calcium propionate and potassium sorbate.

Bacteria produce chemicals called bacteriocins to kill microbial competitors. These chemicals can serve as natural preservatives by killing potentially dangerous pathogens in food. Lanthipeptides, a class of bacteriocins with potent antimicrobial properties, are widely used by the food industry and have become known as lantibiotics.

Despite their widespread use, little is known about how these lantibiotics alter the gut microbiomes of people who consume them in food. Gut microbes live in a delicate balance, and commensal gut bacteria can provide important benefits to the body by breaking down nutrients, producing metabolites and protecting against pathogens. If too many commensals are killed off by antimicrobial food preservatives, pathogenic bacteria might take their place and cause issues in the gut.

A study published in ACS Chemical Biology by scientists from the University of Chicago found that a common class of lantibiotics has potent effects against both pathogens and healthy gut bacteria.

Nisin is a lantibiotic used in everything from beer and sausage to cheese and dipping sauces. It is produced by bacteria that live in mammary glands of cows, but human gut microbes produce similar lantibiotics.

Zhenrun “Jerry” Zhang, PhD, a postdoctoral scholar in the lab of Eric Pamer, MD, the Donald F. Steiner Professor of Medicine and Director of the Duchossois Family Institute at UChicago, wanted to study the impact of such naturally produced lantibiotics on commensal gut bacteria.

According to Zhang, Nisin has been long added to food, but how it affects gut microbes hasn’t yet been studied well.

He and his colleagues mined a public database of human gut bacteria genomes and identified genes for producing six different gut-derived lantibiotics that closely resemble nisin, four of which were new. Then, in collaboration with Wilfred A. van der Donk, PhD, the Richard E. Heckert Endowed Chair in Chemistry at the University of Illinois Urbana-Champaign, they produced versions of these lantibiotics to test their effects on both pathogens and commensal gut bacteria. The researchers found that while the different lantibiotics had varying effects, they killed pathogens and commensal bacteria alike.

“This study is one of the first to show that gut commensals are susceptible to lantibiotics, and are sometimes more sensitive than pathogens,” Zhang said. “With the levels of lantibiotics currently present in food, it’s very probable that they might impact our gut health as well.”

Zhang and his team also studied the structure of peptides in the lantibiotics to better understand their activity, in the interest of learning how to use their antimicrobial properties for good. In another study, the Pamer lab found that a consortium of four microbes, one producing lantibiotics, helped protect mice against antibiotic-resistant Enterococcus infections. The team is also studying the prevalence of lantibiotic-resistant genes across different populations of people to better understand how this bacteria can colonise the gut under different conditions and diets.

“It seems that lantibiotics and lantibiotic-producing bacteria are not always good for health, so we are looking for ways to counter the potential bad influence while taking advantage of their more beneficial antimicrobial properties,” Zhang said.

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