Intestinal Microbes that Harm the Liver: The Microbiota’s Transformation into a Toxic Microbrewery

Imagine: you are a police officer, and you notice a car that zigzues dangerously on the road. You stop the driver: he is clearly drunk. In a pasty voice, he swears that he did not touch a drop of alcohol of the day. Would you believe it? Probably not.

However, in 2024, a Belgian citizen was acquitted after being fined for driving in a state of drunkenness three times in four years. His job in a brewery could feed suspicion, but he said he had drunk nothing. According to the three doctors who auscultated him, he suffered from a self-brasserie syndrome from which he did not know existence.

People with this very rare syndrome (A review of English -language scientific literature published in 2020 revealed that only 20 cases had been identified since 1974, editor's note) Host in their intestines microbes producing abnormally high quantities of alcohol when they break down sugars. In 2016, in New York, a woman was also acquitted after an identical diagnosis. His blood alcohol level reached the legal limit four times.

Although auto-brewery syndrome is exceptional, some of the bacterial species associated with it could be involved in another much less rare disease, hepatic steatosis.

As a microbiologist, I am passionate about studying the various effects of the intestinal microbiota on human health, as well as on mood and behavior, which I also vulgarized in the book Please to meet me: genes, germs, and the curious forces that make us who we are. Here's what you need to know about these bacteria producing alcohol and the suspicions that weigh on them.

A sick liver without alcohol abuse

The accumulation of fats in the liver can cause serious health problems. The resulting chronic inflammation can notably promote the occurrence of liver fibrosis which can lead to cirrhosis, which can play in liver cancer in the long term.

Hepatic steatosis is often associated with alcoholism. However, metabolic hepatic steatosis associated with dysfunction, or Masld, occurs without excessive alcohol consumption. Formerly called “non-alcoholic hepatic steatosis” (shna, or nash in English for non-alcoholic steatohepatitis), and also designated in French by the expression “fatty liver disease”, this condition is a continuum of hepatic anomalies which affects 80 million to 100 million Americans (In France, the consistency cohort data of 2020 indicate that non -alcoholic hepatic steatosis would affect 18.2 % of the population, editor's note).

The causes of the MASLD seem multiple: obesity, resistance to insulin, excess cholesterol or infection by hepatitis C. Works also seem to suggest that certain microbes could also play a role.

In 2019, in particular, doctors identified a patient suffering from both auto-brewery syndrome and a severe Masld. The analysis of its stool revealed the presence of the bacteria Klebsiella pneumoniae. It turned out that the isolated strain produced four to six times more alcohol than those usually encountered in healthy individuals.

Out of 43 other patients with Masld, 61 % hosted a strain of K. Pneumoniae producing unusual amounts of alcohol. On the other hand, among the 48 healthy people serving as witnesses, only 6 % were affected.

Researchers also found that K. Pneumoniae was only slightly abundant in the patient's intestine than in witnesses. It was the amount of alcohol produced that different. They then wondered if this excess could really cause steatosis.

A microbrewery in the intestine?

To verify whether these bacteria were indeed responsible for the situation of patients, scientists led tests on laboratory animals. They have nourished healthy mice with the hyper-alcoholic strain of K. Pneumoniae. In a month, rodents developed measurable steatosis, which evolved into cirrhosis after two months. The progression of the disease faithfully reproduced that observed when the mice was stuffed with pure alcohol.

In addition, the transfer of microbiota from mice or humans with masld in healthy mice has also triggered liver lesions.

Finally, the researchers treated the microbiota of mouse with Masld with a targeting virus only Klebsiellato destroy these bacteria. The transfer of the microbiota thus rid of Klebsiella In healthy mice has caused any disease in the latter.

These results suggest that certain strains of K. Pneumoniae manufacture excessive quantities of alcohol, capable of inducing liver steatosis. They also suggest that certain forms of steatosis linked to Klebsiella May be treated by antibiotics. Indeed, the administration has mice with imipenem, an antibiotic of the family of beta -lactams, of the carbapenema class, reversed the evolution of the disease.

Since K. Pneumoniae Transforms sugar into alcohol, a simple blood test measuring the blood alcohol level after ingestion of sugar could make it possible to diagnose this particular shape of steatosis. Researchers have shown that mice hosting these bacteria became drunk and saw their blood alcohol level climbing after consuming sugar.

It should be emphasized that the magnitude of this phenomenon is not yet known. If Klebsiella is frequently present in the human intestine, we do not know why some people host large quantities of alcohol producing.

More broadly, these works once again illustrate the role of the microbiota in the regulation of mood and behavior. As with the New York driver acquitted, the simple fact of consuming a very sweet dessert could, in rare cases, lead in some people to be intoxicated without having consumed alcohol. The Belgian employee, on the other hand, tries to reduce his intestinal alcohol production by following both a specific diet and drug treatment, according to declarations by his lawyer. It remains to be seen whether these individuals develop increased tolerance for alcohol, by their continuous exposure.