fecal microbiota transplant

fecal microbiota transplant (FMT), procedure in which processed stool from a healthy donor is transferred into the intestinal tract of another person. It attempts to restore balance to a community of intestinal microorganisms that has been disrupted by infection, antibiotic use, or disease. FMT is particularly valuable in the treatment of infections involving Clostridium difficile (or Clostridioides difficile) bacteria, which may be resistant to conventional antibiotics.

FMT works by directly introducing healthy bacterial populations from a donor into a patient’s colon. This intervention corrects dysbiosis, an imbalance caused by such factors as antibiotics that leads to the proliferation of harmful bacteria. The transplanted microbes repopulate the intestinal tract and restore stability to an ecosystem where beneficial flora can effectively outcompete and overtake the pathogenic bacteria, thereby resolving persistent infections.

Historical developments

The idea for FMT originated more than 1,700 years ago in China, where physicians administered fecal preparations from healthy donors to treat severe diarrhea in others. The approach was adopted into Western medicine in the late 1950s, when it was used to treat antibiotic-associated diarrhea, and by the early 1980s it had been found to be particularly effective for infection with C. difficile, which causes colitis (inflammation of the colon) and in severe cases is untreatable. The results of a groundbreaking clinical trial published in 2013 provided definitive proof of FMT’s effectiveness for treating recurrent C. difficile infection (rCDI) that is unresponsive to existing antibiotics. That year FMT was approved by the U.S. Food and Drug Administration (FDA) for the treatment of rCDI. The first orally administered FMT product for rCDI became available a decade later. Today the procedure is being investigated for other conditions, including inflammatory bowel disease, irritable bowel syndrome, and various metabolic diseases linked to an imbalance in the gut microbiome.

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Procedure

FMT begins with screening donor stool for a wide range of pathogens, including disease-causing viruses and bacteria as well as intestinal parasites. Donor screening protocols further include medical history, questionnaires, and additional tests to minimize the risk of disease transmission. Stool samples free of infectious agents are then processed into either a liquid mixture, which can be administered through methods such as colonoscopy, enema, or nasogastric tube, or into capsule form for oral administration.

Safety and regulatory concerns

Side effects of FMT generally appear to be mild; examples include temporary diarrhea, cramping, and bloating. Potential risks, however, are significant. Existing screening methods, although extensive, cannot eliminate all risks associated with live stool samples, and undetected pathogens can have severe consequences. In 2020, multiple patients developed serious infections from antibiotic-resistant E. coli transmitted via FMT, which led to several deaths. The incident prompted the FDA to issue a safety alert on the use of FMT and highlighted a need for more-rigorous donor screening. Even with more-stringent screening protocols, however, newly emerging pathogens can escape detection by existing tests.

Unknown long-term risks and inconsistent regulations have further hindered widespread adoption and standardization of FMT. Studies in animal models and human tissue have shown, for example, that transplanted microorganisms can colonize unintended areas of the gut, altering the local environment, metabolism, and even behavior. Furthermore, there is disagreement on how to classify and regulate the inherently variable and biologically active substance of human feces. Regulation of FMT varies worldwide; for instance, the FDA treats it as a biological product requiring strict approval, whereas European countries apply various rules, such as transplant and medicinal classifications as well as oversight under regulations concerning substances of human origin (SoHO) in the European Union.