Intestine

Useful bacteria: This is how the stomach helps the intestines


Filter function discovered: Stomach specifically enriches and removes microorganisms

In the past, science assumed that stomach acid killed almost all microorganisms. But that is obviously not the case. A study has now shown that the stomach specifically accumulates and depletes microorganisms and releases them to the intestine in a filtered manner.

The composition of the microorganisms in the stomach fluctuates very much

The role of the stomach for the health of the gastrointestinal tract is still a mystery to science: the composition of the microorganisms in the stomach fluctuates very strongly, so far it has only been possible to speculate about the influence of these fluctuations on the intestine. But now a research team from the University of Hohenheim in Stuttgart and the Medical University of Graz have developed a method that can be used to distinguish living, active bacteria from dead ones and determine their quantity.

Important control function

With this method, it was possible for the first time to link fluctuations in the composition of the permanent inhabitants of the stomach with an overall increase in bacteria.

As stated in a statement by the University of Hohenheim, it also became clear that the stomach within the gastrointestinal tract has an important control function on the passage of certain bacteria into the intestine.

The current results have now been published in "mSystems", the journal of the "American Society for Microbiology".

Influence of the stomach on the intestine

Surgical reduction of the stomach in obesity (obesity) has positive properties that cannot be explained by a reduction in the volume of the stomach alone.

For example, insulin resistance may decrease and the resulting regulation of blood sugar levels as well as general inflammation parameters may improve - an effect that is typically associated with processes in the intestine rather than in the stomach.

Similar questions about the influence of the stomach on the intestine raise clinical observations on the side effect of proton pump inhibitors.

These are drugs that inhibit stomach acid production and are among the most commonly prescribed drugs to treat stomach ulcers, heartburn, etc.

But if you take them for a long time, you have an increased risk of developing diarrhea after taking antibiotics.

"Both are indications that events in the stomach lead to changes in the intestinal microbiome," explains Prof. Dr. Florian Fricke, Head of the Department of Microbiome and Applied Bioinformatics at the University of Hohenheim.

"The stomach may provide more opportunities to influence intestinal-related problems than previously thought - in both a positive and a negative sense."

Previous assumption apparently not correct

According to Prof. Fricke, it was previously assumed that stomach acid killed almost all microorganisms.

"Obviously that's not the case. However, we have not yet known what a healthy gastric microbiome looks like and what influence it has on the transfer of microorganisms from the mouth to the intestine, ”said the expert.

"Previous studies of the stomach as well as the intestine were also made difficult by the extremely fluctuating proportions of the various types of bacteria in the microbiome. So far, there has been no explanation for this in healthy people, ”said Prof. Fricke.

New procedure differentiates living and dead bacteria

The problem with classical microbiome research is that the so-called sequence-dependent methods only examine DNA, i.e. the relatively stable molecular carrier of the genetic information of a bacterium.

"With this, they capture living bacteria as well as dead ones - so they cannot differentiate between the microbiome adapted to the stomach and externally registered, inactive bacteria."

Together with his doctoral student Elisabeth Dörner and his colleagues at the Medical University of Graz, Prof. Fricke is therefore developing a new technical approach - and resorting to a trick:

They record not only the DNA, but also the RNA - short strands of nucleic acid, which act as a messenger in the use of genetic information in living cells and can therefore only be found in living, active cells.

The scientists test the method in animal models on stomach samples from laboratory mice. At the same time, the project partners in Graz take samples from a total of 24 patients and send them to Hohenheim for analysis.

The researchers isolate the DNA and RNA separately from all samples and characterize both using PCR analysis, a method for enriching and sequencing genetic material.

"This enables us to determine which bacteria are present in total and which parts of the total bacteria are active," explains Prof. Fricke.

“We can also use this method to determine the quantity of bacteria. We can therefore not only determine the relative percentages of the individual species, but also their absolute amounts. ”

Most of the stomach bacteria from only two groups

The researchers found that around 90 percent of gastric bacteria in mice and humans are made up of only two dominant groups.

One of these groups, the lactobacilli in mice and streptococci in humans, is relatively constant in terms of quantity, while the other group of bacteroidetes fluctuates more strongly.

"It is interesting that the constant group also makes up the active, living bacteria," emphasizes Prof. Fricke.

"One can conclude that it performs more crucial functions for the gastric microbiome, while the short-term fluctuating group may get into the stomach with food or other means, but does not remain active there," said the scientist.

"With our results, we can narrow the focus on the bacteria relevant for the examination of the stomach and the passage into the intestine."

Stomach can affect gut microbiome

In order to get a closer look at the functions of the stomach, the researchers do not limit their sampling to the stomach, but also take one sample from the esophagus, three at different locations on the stomach and one from the duodenum.

"The microbiome is relatively similar everywhere, but there are gradual differences," explains Prof. Fricke.

"We found gradients in certain bacteria, that is, increases or reductions from the esophagus to the stomach, which afterwards, that is, between the stomach and the small intestine, are in opposite directions," reports the expert.

“In the stomach, these bacteria are specifically enriched or depleted. As a portal to the intestine, it thus appears to exercise a control or filter function and can thus influence the intestinal microbiome. "

Recognize risks for the intestine in the saliva

The scientists are currently still carrying out classic basic research.

"We hope that our findings will help us to better understand the relationships between the different parts of the gastrointestinal tract and thus perhaps one day to associate deviations in the microbiome of the stomach or mouth with certain diseases of the intestine," says Prof. Fricke.

“It would then be conceivable, for example, that one day one could recognize and treat risks for the intestine in the saliva. Or that the negative effects of drugs like acid inhibitors in the stomach can be compensated for by simultaneously influencing the microbiome. ”(Ad)

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