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Alcohol-producing gut bacteria could cause liver damage even in people who don't drink

Non-alcoholic fatty liver disease (NAFLD) is the build-up of fat in the liver due to factors other than alcohol. It affects about a quarter of the adult population globally, but its cause remains unknown. Now, researchers have linked NAFLD to gut bacteria that produce a large amount of alcohol in the body, finding these bacteria in over 60% of non-alcoholic fatty liver patients. Their findings, publishing September 19 in the journal Cell Metabolism, could help develop a screening method for early diagnosis and treatment of non-alcoholic fatty liver.

"We were surprised that bacteria can produce so much alcohol," says lead author Jing Yuan at Capital Institute of Pediatrics. "When the body is overloaded and can't break down the alcohol produced by these bacteria, you can develop fatty liver disease even if you don't drink."

Yuan and her team discovered the link between gut bacteria and NAFLD when they encountered a patient with severe liver damage and a rare condition called auto-brewery syndrome (ABS). Patients with ABS would become drunk after eating alcohol-free and high-sugar food. The condition has been associated with yeast infection, which can produce alcohol in the gut and lead to intoxication.

"We initially thought it was because of the yeast, but the test result for this patient was negative," Yuan says. "Anti-yeast medicine also didn't work, so we suspected [his disease] might be caused by something else."

By analyzing the patient's feces, the team found he had several strains of the bacteria Klebsiella pneumonia in his gut that produced high levels of alcohol. K. pneumonia is a common type of commensal gut bacteria. Yet, the strains isolated from the patient's gut can generate about four to six times more alcohol than strains found in healthy people.

Moreover, the team sampled the gut microbiota from 43 NAFLD patients and 48 healthy people. They found about 60% of NAFLD patients had high- and medium-alcohol-producing K. pneumonia in their gut, while only 6% of healthy controls carry these strains.

Jing Yuan, et. al. Fatty Liver Disease Caused by High-Alcohol-Producing Klebsiella pneumoniae. Cell Metabolism, 2019; DOI: 10.1016/j.cmet.2019.08.018

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