Scientists believe some people's poo might contain an ideal mix of healing bacteria to fix gut diseases, making them super-donors.
Our guts house millions of bugs that live inside us as a community. This diverse microbiome is unique to each us - no two are exactly the same.
"Super donors" — people whose stool donations have strikingly high success rates in poo transplants — have turned up in multiple studies, according to a review paper published in Frontiers in Cellular and Infection Microbiology.
And while a large part of the super-donor effect is likely down to the community of bugs dwelling in a person's gut, known as the gut microbiome, it's certainly not the be-all and end-all.
Faecal microbiota transplants, also known as FMTs or poo transplants, take a sample of faeces from a healthy person and "transplant" it into the intestines of a person with an infection or disease.
The transfer of faeces from one individual into another has become a useful treatment for recurrent Clostridium difficile (C Diff) infections. Such infections are bacterial over-growths in the gut that are often resistant to antibiotics and can cause severe diarrhoea, said Justin O'Sullivan, University of Auckland microbiologist and paper co-author.
Clostridioides difficile, also known as C. difficile, C. diff, or sometimes CDF/cdf, is a species of Gram-positive spore-forming bacterium. Clostridioides are anaerobic, motile bacteria, ubiquitous in nature, and especially prevalent in soil.
However, the procedure is also showing promise for a host of other conditions, including ulcerative colitis (an inflammatory bowel disease), that have been also been linked to the microbiome of the gut– the community of bacteria, viruses and fungi found there – being out of kilter.
The idea is that by introducing a diverse dose of microbes via poo transplant, C. difficile must compete for gut real estate, bugs will "take hold" and restore the host's microbiota to a healthy state. Symptoms can clear up within a few hours.
"It's an over-90-per-cent cure rate. It's incredible," Dr O'Sullivan said.
While it might seem a relatively modern clinical treatment, the first poo transplants were documented by Chinese doctors as far back as the fourth century.
Schematic representation of the role of the gut microbiota in health and disease giving some examples of inputs and outputs. CVD=cardiovascular disease; IPA=indolepropionic acid; LPS=lipopolysaccharide; SCFA=short chain fatty acids; TMAO=trimethylamine N-oxide
He says a larger number of species in the donor's stool has been shown to be one of the most significant factors influencing faecal transplantation outcome. And patients who respond well to the transplants develop a more diverse microbiome too.
Studies have shown that while success rates for procedures to treat C Diff are similar regardless of the stool donor, some conditions – including ulcerative colitis – were improved depending on the donor.
In one study the remission rate for ulcerative colitis was twice as high among recipients whose transplant included stool from one particular donor. Such results have fuelled the emergence of an unlikely sounding hero: the super-donor.
What constitutes a "good" or "healthy" gut microbiota isn't entirely clear. Nor what makes a poo donor "super".
There's a general idea that a super donor's microbiota has more bacterial diversity as well as a few "keystone" species that seem to benefit gut health. "You have fungi, protozoa and viruses there as well and they can change the bacterial populations."A virus that attacks one species of bacteria, for instance, will modify the gut microbe community.
Researchers strained stools and dispensed the filtered fluid, or filtrate, in patients with C. difficile and found tha, what's floating around the microbes' environment, such as bits of bacterial debris, DNA and proteins, seems to help restore gut health too.
"Filtrates don't have the actual bacteria in them, but they also see clinical resolution," Dr O'Sullivan said.
Still, no matter how "super" a donor's stool sample is, its success is also highly dependent on the recipient. What they eat, for instance, might help or hinder a poo transplant.
Transplanted microbes also need to be able to integrate with the existing residents.
If a recipient's immune system attacks the introduced species, they may not see as much benefit.
There's probably a genetic component too, but as Dr O'Sullivan and his colleagues point out in their paper, this is hard to tell yet as few studies collected genetic information.
Its a very multifaceted environment to analyse and understand. As microbiologists continue to uncover the mechanisms behind the super-donor phenomenon, they might find a whole range of super donors specific to certain diseases.
Anybody wishing to donate to the FMT bank at Guy's and St Thomas' Hospital should contact simon.goldenberg@gstt.nhs.uk