Yes, I know the idea of faecal, (stool) transplants makes you feel squeamish.
But while a few years ago only a handful doctors were carrying them out – and then only as a last resort – research has proved they’re very effective against the potentially fatal infections caused by the microbe C. difficile.
Now the treatment which involves transplanting stool bacteria from a healthy donor to a recipient, is done almost weekly in some centres.
And we’re discovering faecal transplants can attack a broader spectrum of disease than we first thought.
Scientists are currently testing them against such diseases as ulcerative colitis, even obesity and diabetes.
Yet for all the excitement, scientists still know surprisingly little about why they work.
A gram of stool contains a staggering mix of approximately 100 billion bacteria, 100 million viruses and a million spores of fungi.
That gram also contains 100 million microbes known as archaea – distant relatives to bacteria.
“There’s a lot going on in there – it’s a whole community,” says Frederic D. Bushman, a microbiologist at the University of Pennsylvania, USA.
But how do faecal transplants work?
Stool bacteria from healthy people seem to help patients in a few different ways. “We understand, sort of, how they work,” says Dr Vincent B. Young, an infectious diseases physician at the University of Michigan Medical School.
In a healthy gut, different species struggle with their rivals for territory.
“They have to compete for space, because it’s a nice place to be,” says Dr Alexander Khoruts, a gastroenterologist at the University of Minnesota, USA.
The bacteria from a donor’s healthy gut may be superior at competing for that space.
They may also be able to gobble up nutrients that competing invaders like C. difficile need to survive.
But it’s also possible that other microbes are involved in ways that doctors just haven’t considered.
“Bacteria have gotten all the limelight,” Dr Bordenstein complains.
Dr Bushman and his colleagues have shown that viruses can survive transplants.
“Maybe they’re making the bacterial community more diverse by whacking back any one that grows out too much,” he says.
These insights may let doctors develop safer, more effective methods to use microbes in treating a range of diseases.
A pill containing just a few effective species of bacteria, viruses or other organisms might be safer than stool delivered through an enema.
Still, it’s often hard to improve on nature. It may also prove difficult to outdo our own stool.
“This is something nature put together over millions and millions of years,” Dr Khoruts says.