Gut Microbial Enterotypes Form a Spectrum Rather than Distinct Groups

Bacteroides fragilis, part of the intestinal flora

Trillions of bacteria populate our intestines. While these communities vary between humans, a study published last year in the journal Nature indicated that they may fall into just three distinct types. However, new data presented at the International Human Microbiome Congress in Paris suggests that the boundaries between enterotypes are fuzzier than previously thought.

Each of the three enterotypes was characterized by high levels of a single microbial genus, Bacteroides, Prevotella, and Ruminococcus.

Cell surface structures of Prevotella intermedia strains 17 (A) and 17-2 (B).

Manimozhiyan Arumugam, molecular biologist at the European Molecular Biology Laboratory in Heidelberg, Germany, the author of the original paper, and his team repeated the analysis of 663 Danish and Spanish adults.

The results show that a genus of archae, called Methanobrevibacter, joins Ruminococcus as a defining microbe in the third enterotype. The separation between this cluster and Bacteroides is no longer clear. However, they remain distinct from the Prevotella.

Dan Knights, a computational biologist at the University of Colorado at Boulder, told the conference that discrete enterotypes may not exist at all. His team studied the intestinal flora of 1,200 adults and found a continuum of communities, from Bacteroides-driven ones to Prevotella-driven ones. His results will be published in the journal PLoS Computational Biology.

There is a gradient and the enterotypes are concentrated within that, states Knights. The boundaries may be blurred but the differences between the extremes are still there. The actual structure within this gradient is what needs to be defined as well as studying the microbial flora of more people.

Enterotypes might affect how much a person is at risk of disease or responds to different drugs. Last year in the journal Science, it was discovered that the Bacteroides enterotype is associated with diets high in fat or protein while Prevotella is associated with a high-carbohydrate diet.