This short video explores the science behind fecal microbiota transplants, a method of transplanting stool from healthy donors to sick patients to treat certain diseases.

A healthy intestinal tract is teeming with trillions of microbes, which generally keep us infection-free by fending off attacks from disease-causing bacteria. But sometimes, harmful bacteria like Clostridium difficile (C. diff) can grow in large numbers in the intestine, causing chronic and painful diarrhea, or even death. Doctors typically treat C diff-infected patients  with an intensive course of antibiotics, but this can weaken individuals’ gut microbiome and leave them susceptible to further infection. Some doctors are treating patients who aren’t helped by standard antibiotics with fecal transplants, which have yielded remarkable recovery rates.

This video is part of the series I Contain Multitudes, hosted by science journalist Ed Yong.