Food additives like nisin open doorway for pathogens to weaken microbiome, experts flag

09 Feb 2024 --- Researchers from the University of Chicago, US, scoured a database of human gut bacteria genomes and discovered that common classes of lantibiotics — a set of peptide antibiotics containing unique amino acids — have potent effects against pathogens and commensal gut bacteria. 

Commensal gut bacteria degrade food in the intestine to supply energy to the cells and are necessary to keep humans healthy. The scientific analysis focused on nisin, a common preservative used to kill pathogens in food and observed that it has an adverse effect on beneficial bacteria, which can threaten the balance of the gut microbiome.

When too many commensals are killed off by antimicrobial food preservatives, opportunistic pathogenic bacteria could take their place and “wreak havoc,” causing similar effects to eating contaminated food.

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

Killing off microbial competitors
Food manufacturers regularly add preservatives to food products to keep them fresh. The purpose of the preservatives is to kill microbes that could break down and spoil the food. Sugar, salt, vinegar and alcohol are common additives that have been used for its preservative function for centuries.However, modern food labels tend to use sodium benzoate, calcium propionate and potassium sorbate.

Nisin, for example, is a popular lantibiotic used in beer, sausage, cheese and dipping sauces, among others. It is produced by bacteria that live in the mammary glands of cows, but microbes in the human gut produce similar lantibiotics too. 

Bacteria produce chemicals called bacteriocins that kill microbial competitors. These chemicals can serve as natural preservatives by killing potentially dangerous pathogens in food. Commensal bacteria break down nutrients, produce metabolites and protect against pathogens.While food additives preserve food, little is scientifically known about its effects on the gut microbiome.  

“Nisin is, in essence, an antibiotic that has been added to our food for a long time, but how it might impact our gut microbes is not well studied. Even though it might be very effective in preventing food contamination, it might also have a greater impact on our human gut microbes,” says Zhang.

Mining gut bacteria genomes
The researchers mined a public database of human gut bacteria genomes and identified genes for producing six different gut-derived lantibiotics that resemble nisin and four new ones. Their findings were published in ACS Chemical Biology.

They produced various versions of the lantibiotics to test its effects on pathogens and commensal gut bacteria. The researchers found that while the different lantibiotics had varying effects, they killed pathogens and commensal bacteria alike.

The scientists also studied the structure of peptides in the lantibiotics to better understand their activity to learn how to beneficially use their antimicrobial properties. 

“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 explains.

The researchers are also studying how rife lantibiotic-resistant genes are across different populations of people to better understand how the bacteria can colonize the gut under different conditions and diets.

In addition, a recent study conducted by researchers at the Washington University School of Medicine, US, found that the bioactive glycans found in microbiome-directed complementary food for children with malnourishment are more effective at repairing the gut microbiome than the transitionally used therapeutic food.

By Inga de Jong