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Kimchi and artisan cheeses can contain antibiotic-resistant bacteria


Kimchi, a traditional Korean dish made with salted and fermented vegetables, can contain antibiotic-resistant bacteria

Magdalena Bujak/Alamy

Fermented food such as kimchi and artisan cheeses can contain antibiotic-resistant bacteria, some of which have the potential to cause ill health.

For more than 20 years, Hua Wang at The Ohio State University in Columbus has been working with manufacturers of fermented products, such as cheesemongers, to ensure they are free of antibiotic-resistant microbes.

In her latest research, Wang and her colleagues looked for such microbes in 10 types of kimchi – a traditional Korean dish made with salted and fermented vegetables – and four artisan cheeses, bought from either local or national retail stores, or Japanese or Korean restaurants, in the Columbus, Ohio, area.

The team found that nine of the kimchi products and all of the cheeses contained antibiotic-resistant bacteria, some of which have the potential to cause gut-related symptoms or more severe health issues if they enter the bloodstream. These also contained a variety of lactic acid bacteria, which drive fermentation, that were similarly resistant to some antibiotics.

Fermentation bacteria can acquire or develop resistance to antibiotics. However, that would only be a problem if they caused an infection or transferred the antibiotic-resistance gene to another bacterium, which “is possible but hasn’t yet been shown”, says Mark Turner at the University of Queensland in Australia, who wasn’t involved in the research.

But one of the retail-bought kimchi products the researchers tested contained a strain of Weissella, a type of fermentation bacteria that they found was highly resistant to antibiotics. “If these strains get into the bloodstream through gastrointestinal tract issues, they can cause bacteraemia [a bloodstream infection] or sepsis, untreatable by antibiotics,” says Wang. “This is regardless of the transfer of antibiotic resistance genes in the gut.”

In another part of the experiment, the team made some kimchi samples. “These also invariably contained antibiotic-resistant strains of microbes,” says Wang. Such bacteria may be on the raw vegetables or in the water used to make the dish, with fermentation accelerating their growth, she says.

The mainstream dairy industry often uses pasteurised milk, along with starter cultures – bacteria grown to kickstart the transformation of milk into cheese – that have been screened for antibiotic-resistant pathogens, the researchers write in their paper. More artisan manufacturers, however, may use unpasteurised milk and cultures that haven’t been screened.

Finally, the team reassessed genetic data from a previously published study. Out of 36 adults, half were told to eat a diet high in plant-based food, while the other half ate a diet rich in fermented food. After 10 weeks, those who ate more fermented food had an increase in the level of genes associated with antibiotic-resistant bacteria in their stools. There was no change in the non-fermented food group.

People with issues affecting their digestive tracts or immune systems could become ill after ingesting these microbes, says Wang. Many people also turn to fermented food after a course of antibiotics or an illness, in an effort to reset their gut health. These individuals may be most at risk when consuming fermented food with antibiotic-resistant bacteria, says Wang.

What’s more, ingesting such microbes could worsen the antibiotic resistance crisis when they enter the environment via faeces.

Wang expects similar results to apply to other homemade or artisan fermented food and drinks, such as sauerkraut, made with raw cabbage, and kombucha, black tea made with a symbiotic culture of bacteria and yeast (SCOBY).

Off the back of this research, Wang has urged people to be cautious if they are making fermented food. They should opt for screened starter cultures and pasteurised milk, she says.

“Antibiotic resistance is a major issue that humankind is facing, especially bacteria that have developed resistance to last-line antibiotics,” says Turner.

Without screening starter cultures, fermentation is “spontaneous” rather than “controlled”, so “there is a greater chance of undesirable bacteria species or bacteria carrying antibiotic resistance genes entering the fermented food”, he says.

Topics:

  • antibiotics/
  • food and drink



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