With the importance of gut microbiota on our health becoming clearer, you'd be forgiven for wanting to run to the nearest health food store and grab all the probiotic supplements you can lay your hands on. But improving your gut health may not be so simple, with researchers in Israel finding that the digestive tract of many people can prevent probiotics from colonizing one's gastrointestinal tract. Additionally, consuming probiotics as a counterbalance to any antibiotics being taken could delay normal gut bacteria returning to their original state.

To explore the benefits of probiotics in people, researchers at the Weizmann Institute of Science and the Tel Aviv Medical Center conducted a couple of experiments. The first study involved 25 human volunteers who were given endoscopies and colonoscopies to sample their baseline microbiome in regions of the gut. Fifteen of the volunteers were then split into two groups, with the first consuming generic probiotic strains and the second given a placebo. Both groups were then given another round of upper endoscopies and colonoscopies to gauge their internal response, before they were tracked for another two months.

The researchers found that the probiotics successfully colonized the gastrointestinal (GI) tracts of some people, which are dubbed "persisters," while they were expelled by the gut microbiomes of others, dubbed "resisters." The researchers claim it was possible for them to predict whether an individual was a persister or resister just by looking at their baseline microbiome and gut gene expression profile, with the persister and resister patterns determining whether probiotics would impact that person's indigenous microbiome and human gene expression.

The use of endoscopies and colonoscopies differed from previous studies, which generally used a person's stool as a proxy for microbiome activity in the GI tract. The team found that relying on a patient's excrement could be misleading because it only correlated partially with the microbiome functioning in the body.

"Although all of our probiotic-consuming volunteers showed probiotics in their stool, only some of them showed them in their gut, which is where they need to be," says Eran Segal, a computational biologist at the Weizmann Institute. "If some people resist and only some people permit them, the benefits of the standard probiotics we all take can't be as universal as we once thought. These results highlight the role of the gut microbiome in driving very specific clinical differences between people."

The second study set out to explore the effects of taking probiotics to counter the effects of antibiotics – a common practice thought to help in repopulating the gut microbiota after a round of antibiotics. It involved 21 volunteers being given a course of antibiotics before being split into three groups. The first group's microbiome was left to recover on its own, while the second group was given the same generic probiotics used in the first study twice daily for a period of four weeks. Meanwhile, the third group was given an autologous fecal microbiota transplant (aFMT), which is stool collected from the same individual before they received the antibiotic.

After the antibiotics had provided a clean canvas, the team found the standard probiotics were able to easily colonize the gut of all members of the second group. However, this came with a trade-off in the form of a delay of months before the host's microbiome and gut gene expression profile returned to normal. Conversely, the native gut microbiome of the third group that received the aFMT took only a few days to return to normal. It took the gut microbiota of the first "watch-and-wait" group longer than the aFMT group, but less time than the standard probiotic group, to return to normal.

"Contrary to the current dogma that probiotics are harmless and benefit everyone, these results reveal a new potential adverse side effect of probiotic use with antibiotics that might even bring long-term consequences," says senior author Eran Elinav. "In contrast, replenishing the gut with one's own microbes is a personalized mother-nature-designed treatment that led to a full reversal of the antibiotics' effects."

Segal says that the research could take probiotic consumption from a universal approach, which often looks to be useless, to a more tailored approach based on an individual's baseline features.

Both studies appear in Cell Press [1], [2].

Source: Cell Press