The effect of probiotic preparations varies from person to person, and may even be undesirable

"The results of the study indicate that probiotics should not be administered to the general public. It must be adapted to each person according to his personal needs" say researchers Eran Alinev and Eran Segal from the Weizmann Institute

Millions of people around the world take probiotics every day - preparations containing live bacteria designed to strengthen the immune system, prevent diseases or correct the negative effects of antibiotics. However, the benefits of probiotics have never been scientifically proven. Moreover, it is not at all clear whether the probiotic bacteria introduced into the body succeed in colonizing the digestive system, and if so, how they affect humans and their microbiome - the population of bacteria residing in our bodies. From two new studies by Weizmann Institute of Science scientists published simultaneously in the scientific journal Cell, shows that the effect of 11 strains from the most common probiotic bacteria families varies from person to person, and may even be undesirable in some people.

In the first study, 25 volunteers underwent endoscopy and colonoscopy in order to sample their microbiome and establish its basic composition and its activity in the different areas of the intestines. 15 of the volunteers were divided into two groups: the first received the probiotic preparation, and the second received a dummy pill (placebo). Three weeks after the start of the treatment (which lasted four weeks in total), all participants underwent a second endoscopy and colonoscopy to confirm the changes that had occurred in their bodies, and remained monitored for another two months.

The researchers from the laboratories of Prof. Eran Alinev from the Department of Immunology and Prof. Eran Segal from the Department of Computer Science and Applied Mathematics, discovered that the degree of intestinal colonization of the probiotic strains varied significantly from person to person. However, they noticed two main groups: the group of "persisters" in whose intestines the probiotic bacteria settled, and the group of "resisters" who eliminated the guests. The research team discovered that it is possible to predict which of the two groups a subject will belong to based on the basic composition of his gut bacteria and the gene expression profile in his digestive system. The study was conducted in collaboration with Prof. Zamir Halpern, Director of the Gastroenterology Division at the Tel Aviv Sorasky (Ichilov) Medical Center.

"The results of the study indicate that probiotics should not be given to the general public," says Prof. Alinev, "each person should be adapted according to their personal needs." Prof. Segal adds: "The results add to our previous findings, which revealed a personal response to food, and emphasized the role of the gut microbiome as a source of unique clinical differences between humans."

In the second study, the researchers referred to the conventional combination of antibiotics and probiotics. Many times we are advised to take probiotics in order to deal with the negative effects of antibiotics. Following antibiotic treatment, do the probiotic bacteria settle in the intestine more easily, and if so, what is their effect on the host body and its microbiome? The researchers gave broad-spectrum antibiotics to 21 volunteers, who then underwent endoscopy and colonoscopy to examine changes in their gut and microbiome. Later, the volunteers were randomly divided into three groups: the first - the "wait and see" group, in which the microbiome in the body was allowed to recover on its own; The second group received the preparation of the 11 probiotic strains over a period of four weeks, and the third group was treated with "self-implantation of feces", which was collected from the subjects before the antibiotic treatment.

The researchers discovered that after antibiotic treatment, the probiotic bacteria settled relatively easily in the intestine - certainly compared to the findings in the previous study, where no antibiotics were given. However, to the researchers' surprise, colonization prevented the gene expression profile and the microbiome from returning to their original, pre-antibiotic configuration for many months. Autologous fecal transplantation, on the other hand, resulted in the resettlement of the original microbiome and the return of the gene expression profile to normal within days. "These findings," says Prof. Alinev, "reveal a new and worrying side effect of using probiotics combined with antibiotics, which may have long-term consequences. On the other hand, personalized treatment - using the patient's own bacteria for the purpose of replenishing the stock of bacteria in the intestine - completely canceled the effect of the drugs."

Since probiotics are one of the best-selling food supplements in the world, the research findings may have extensive and immediate implications. "Contrary to the existing belief, according to which probiotics are not harmful and even beneficial," says Prof. Segal, "we suggest adjusting probiotic preparations to patients personally, or in some cases, considering treatments such as fecal transplantation."

Dr. Niv Zamora, Yotam Suetz, Gili Zilberman-Shapira and Uriah Mor from Prof. Alinev's laboratory led the two studies, in collaboration with Dr. Meli Dori-Baksh, Dr. Stavros Bashards, Maya Tzur, Dana Regev-Lehavi, Rotam Ben -Zev Barik, Dr. Sara Federici, Yotam Cohen, Max Horn, Rachel Linevsky, Dr. Mirav Pevsner-Fischer and Dr. Hagit Shapira from Prof. Alinev's laboratory; Dr. Eran Kotler, Dafna Rothschild, Dr. David Zaevi and Dr. Tal Korem from Prof. Segal's laboratory; Andreas Mor, Shani Ben-Moshe, and Dr. Shalu Itzkowitz from Dr. Itzkowitz's laboratory; Prof. Alon Harmelin from the Department of Veterinary Resources, Dr. Nitzan Maharshek and Prof. Oren Shibulat from the Souraski Tel Aviv Hospital, and Dr. Itai Sharon from Tel Hai College and the Migel Institute in the Galilee.