Humans can be grouped by different gut bacteria

European researchers have discovered that gut bacteria in humans can be identified in three distinct groups. As one of these groups is unique in each individual, this finding has implications comparable to the ABO system used to characterize blood types.

Bacteria make up the majority of the microorganisms that live in the human gut. Comprised of approximately 500 species and over 1,000 trillion individuals, bacteria outnumber the cells in the human body 10 to one. They are chiefly responsible for digestion of nutrients and protection against other dangerous organisms that can enter our bodies when we eat.

The researchers, in their article published last month in Nature, aimed to analyze the specifics of the diverse bacterial population of the gut. Using the fecal samples of 22 individuals from Denmark, Italy, Spain and France the group analyzed the DNA of every individual bacterial species by sequencing every single gene. This data was combined with previous DNA analysis of gut bacteria from 13 Japanese and four American individuals.

Their major observation is that there are three distinct clusters of bacteria called “enterotypes,” only one of which was found in any individual sample. By comparing their results to those from the American and Japanese samples, they found that there were no limitations on the enterotypes based on country, continent, age, ethnicity, gender or weight.

However, one limitation of this data is that there are no samples from individuals from South America, Africa, mainland Asia or Australasia. This therefore does not support an assumption that these three enterotypes are universal, as it is possible that more may exist in these areas of the world.

The researchers also found that each of these enterotypes was dominated by a distinct bacterial genus (a classification used to group related species) — Bacteroides, Prevotella and Ruminococcus. They were also unique in the types of food they digest, as well as the pathogens and bacteria they protect us from.

This research constitutes a major step forward in analyzing the huge community of organisms that live inside the human gastrointestinal tract. Previous studies have been unable to pinpoint the exact species of every microorganism that lives inside our bodies and helps us survive. This is due to the complexity of analyzing hundreds of genomes, isolating thousands of individual microbes and sifting through the differences that arise because of the variety of physiological, nutritional and environmental differences among humans.

While the researchers point out that the enterotype system has been compared to the blood group system, they point out that it is highly likely that the bacterial composition of our guts change during our lifetime as the nutritional requirements of our bodies change from infancy to adulthood.