Scientists from the Technion – Israel Institute of Technology and Boston Children’s Hospital have discovered that probiotic consumption may lead to blood infections. Published in Nature Medicine, the study is based on a collaboration between Technion scientists Professor Roy Kishony and Dr. Idan Yelin and research groups led by Professors Gregory Priebe and Thomas Sandora from Boston Children’s Hospital. According to the results of the study, in certain cases, the risk of taking probiotics may outweigh the benefits.

Administering probiotics is a common protocol during medical treatments, and its use in hospitals is constantly expanding as a means for preventing diarrhea and intestinal diseases, and sometimes against pneumonia, pancreatitis, and sepsis.

It now appears consuming probiotic bacteria may result in serious side effects. The study by the research team explored the possibility that these same bacteria find their way to the bloodstream and cause an infection. The hypothesis that probiotics may have harmful effects was raised in the past, but until now no decisive evidence had been presented that proved a causal link. But by using advanced whole-genome mapping technology, the Technion and Boston Children’s Hospital scientists showed that in some cases, infection-causing bacteria do originate in the probiotics administered to the patient.

The research is based on data collected over a 5 1/2 -year period from patients being treated at Boston Children’s Hospital’s Intensive Care Unit. During this period, the ICU treated 22,174 patients, of whom 552 received probiotic capsules as part of their treatment. These consisted of Lactobacillus rhamnosus LGG, one of the most common bacteria strains used in probiotics.

During the study, all six patients diagnosed with Lactobacillus rhamnosus blood infections were part of the group who received probiotic treatments. Among the thousands of patients who did not receive probiotics, none was diagnosed with this type of blood infection.

In their article in Nature Medicine, the scientists provide evidence that the source of the blood infection was indeed the probiotic bacteria. They used innovative genomic tools to prove the infection-causing bacteria originated in the probiotic. The DNA sequences of the bacteria from the infections were fully extracted at the Technion Genome Center, along with the DNA of bacteria from the probiotic capsules. This showed that the bacteria in the blood also contained LGG. Further analysis of the data revealed that the bacteria in the capsules and in the blood cannot be genetically separated. Furthermore, the limited genetic variety found in the capsules was also found in blood isolates. Some of these bacteria found in the bloodstream were new mutations that were not identified among the capsule bacteria, including a mutation that imparts resistance to antibiotics that was found in an isolate from one of the patients. In other words, in addition to the risk of infection, probiotic consumption may also trigger the growth of bacteria resilient to antibiotics — one of the processes that harms the effectiveness of medical treatments and endangers the patient.

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