Friendly gut bacteria that make their own alcohol may seem like the life of the party. But they could be dangerous friends to have.
These ethanol-producing microbes may cause nonalcoholic fatty liver disease, researchers report September 19 in Cell Metabolism.
Fatty liver disease results when too much fat is stored in the liver, and can lead to severe inflammation, liver damage and cancer. The disease, which affects about a quarter of people in the United States, is associated with obesity, type 2 diabetes and high cholesterol. Heavy alcohol drinking can lead to fatty liver disease, but it’s been less clear why nondrinkers or people who drink moderately develop the condition.
Previous studies have implicated gut microbes in the disease. So Jing Yuan of the Capital Institute of Pediatrics and the Chinese Center for Disease Control and Prevention in Beijing and colleagues examined bacteria from the feces of 48 healthy people and 43 with nonalcoholic fatty liver disease, including 32 who suffered from a severe form of the disease called nonalcoholic steatohepatitis, or NASH.
Both groups had similar levels of gut bacteria called Klebsiella pneumoniae in their stools. But in 61 percent of people with nonalcoholic fatty liver disease, the bacteria churned out high and medium levels of alcohol. Only 6.25 percent of healthy people carried the mid- to high-alcohol-producing bacteria.
When the researchers transplanted gut bacteria including alcohol-churning K. pneumoniae from a person with NASH into mice, the rodents also developed fatty livers and inflammation. But selectively killing the alcohol-producing bacteria before the transplant resulted in no liver problems.
These findings suggest that bacterial brewers may be contributing to liver disease in some people.