Unique alcohol-producing gut bacteria can intoxicate and cause liver disease
Inspired by the strange case of a patient with liver damage who consistently became incredibly drunk after eating high-carbohydrate meals, a team of Chinese scientists has discovered specific strains of gut bacteria can produce high levels of alcohol in the body, playing a role in the onset of non-alcoholic fatty liver disease (NAFLD).
Auto-brewery syndrome (ABS) is a very rare condition whereby patients develop high blood alcohol concentrations spontaneously after consuming alcohol-free, high-carbohydrate meals. A strain of yeast has traditionally been thought to be responsible for the condition, essentially fermenting malabsorbed carbohydrates in a person’s bowel. This new study was initiated after researchers examined a patient suffering from an extreme case of ABS with severe liver disease.
"We initially thought it was because of the yeast, but the test result for this patient was negative," says Jing Yuan, lead author on the study. "Anti-yeast medicine also didn't work, so we suspected [his disease] might be caused by something else."
Studying the patient's gut microbiome revealed several highly unique strains of a relatively common bacterial species called Klebsiella pneumonia. Two particular strains of the bacteria were isolated, with the researchers suggesting these had the ability to produce four to six times as much alcohol as strains found in healthy people.
"We were surprised that bacteria can produce so much alcohol," says Yuan.
Non-alcoholic fatty liver disease (NAFLD) is a condition characterized by abnormal fat accumulation in the liver. As the name suggests, unlike other forms of fatty liver disease often primarily caused by excessive alcohol consumption, NAFLD is much more heterogenous, meaning a number of disparate factors can contribute to the condition.
The finding that certain strains of Klebsiella pneumonia can produce high volumes of endogenous alcohol led the researchers to hypothesize the bacteria playing a role in the onset of NAFLD. So microbiome samples from 43 NAFLD patients were examined and the researchers indeed discovered around 60 percent of the patients had these bacterial strains. This compared to only around six percent of a healthy control group displaying the same alcohol-producing gut bacteria.
The final step in the research was to examine whether these Klebsiella pneumonia strains could actually cause NAFLD. Several mouse studies indeed revealed NAFLD could be directly induced simply through the presence of these alcohol-producing Klebsiella pneumonia strains. And, when an antibiotic was administered, killing the negative bacteria, some liver disease symptoms could be reversed.
The fascinating study raises a whole host of new questions that the researchers hope to answer in the future. For example, what factors make a gut environment most hospitable to these particular bacterial strains?
"It's likely that these particular bacteria enter people's body via some carriers from the environment, like food," says co-author Di Liu. "But I don't think the carriers are prevalent – otherwise we would expect much higher rate of NAFLD. Also, some people may have a gut environment that's more suitable for the growth and colonization of K. pneumonia than others because of their genetics.”
And another intriguing question raised by the discovery of this particular bacteria, do human carriers have an unusually high tolerance for alcohol? After all, they would most likely display constant low-blood alcohol levels, so does this explain why that certain friend you have seems able to drink so much more that others while remaining relatively sober?
"Having these bacteria in your gut means your body is exposed to alcohol constantly,” says Liu. "So does being a carrier mean you would have higher alcohol tolerance? I'm genuinely curious!"
The new research was published in the journal Cell Metabolism.