Scientists have figured out why some feces sink, while others do not

(ORDO NEWS) — During experiments with gnotobiotic mice, which are kept in sterile conditions from birth and never encounter microbes in their lives, the researchers noticed that none of the samples of feces of such sterile animals floats, but immediately sinks. And this prompted them to an interesting idea.

Employees of the departments of experimental pathology, gastroenterology and laboratory medicine at the American Mayo Clinic, one of the largest private medical and research centers in the world, managed to find the answer to the old question: why in one case the feces are easily washed away with water, while in the other it continues to float?

Until about the 1970s, experts were sure that this was due to the amount of fat contained in the feces. Moreover, its excess in the feces (more than seven grams per day) – steatorrhea – indicates a violation of the processes of digestion and absorption.

However, according to scientists, the feces of more than ten percent of even healthy people float, and this is not associated with any specific pathology.

Previous studies have shown that the difference in so-called fecal flotation is also related to the amount of gas. However, it was not clear why some people’s excrement contains more gas and is more buoyant than others?

Feces are an excellent sample for studying the intestinal microflora. They represent the largest reservoir of microorganisms, on the order of 100 billion per gram.

In a healthy adult, intestinal gases produced by endogenous microorganisms – in particular, methane, hydrogen sulfide, ammonia – make up only a small amount compared to the bulk of gases, mainly oxygen, nitrogen and carbon dioxide, formed daily in the intestines.

The colon serves as the main source of endogenous gases due to the higher density of the microbiota, which ferment foods containing indigestible carbohydrates.

These fermented gases accumulate and are periodically excreted, but may also be retained in the fecal biomass, thereby reducing the specific gravity of the feces. Therefore, faecal weight can be influenced by lifestyle, diet, water and gas composition, and gut microflora.

While examining the microbiome of gnotobiotic mice living in sterile chambers, the scientists “luckily” found that the faeces of such laboratory rodents and their relatives colonized with intestinal bacteria behave differently in water.

It turned out that the specific gravity of the excrement of mice that were not kept in sterile conditions was much lower, so they swam rather than drowned.

“We used these differences to test with a new method, namely the levô in fimo test (LIFT), to distinguish the sinking fecal pellets of sterile mice from the floating fecal pellets of mice colonized with intestinal bacteria.

By introducing microorganisms into the intestines of sterile rodents, we were able to physically change the properties of feces from “sinking” to “floating,” the scientists said.

Scientists have figured out why some feces sink while others do not
Illustration showing the role of gut microbiota in “fecal floatation” in mice

From this, they concluded that “fecal floatation” is related to the microbiome and the nature of the microorganisms themselves – some produce more gas than others.

The gut of a healthy mouse contains 37 major genera of bacteria that affect the host’s metabolism and immune system. Bacteroides , Gram -negative anaerobic rod-shaped bacteria, is one of the predominant major genera in both mouse and human faecal samples.

And it is the representatives of this genus, including B. ovatus and B. fragilis, that produce hydrogen and carbon dioxide, and the former are still known to provoke flatulence in humans.

“Metagenomic analysis of mouse faeces revealed four gasogenic species of the genus Bacteroides . In fact, we single out Bacteroides ovatus as the most represented species in our analysis. In addition, we have identified Bacteroides fragilis ,” the researchers elaborated.

Of course, more research is needed to better define the different microbial communities that produce more gases, as well as to understand how much of them becomes a decisive factor in the buoyancy of faeces in rodents and humans.

In addition, the question remains unresolved: is all of the above associated with functional bowel diseases?

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