Poo transplants: which bacteria work to treat a type of inflammatory bowel disease?

Fecal microbiota transplantation – or poo transplants – can be an effective treatment for gut conditions. Now, UNSW Sydney medical researchers and collaborators from Australia and the US have shown which bacteria work best.

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A UNSW study into poo transplants has identified the types of bacteria that help treat people with ulcerative colitis. These findings could be used in the design of future microbe-based therapies.

Fecal microbiota transplantation (FMT) – colloquially referred to as ‘poo transplants’ – is an effective treatment for patients with ulcerative colitis (UC), a chronic, inflammatory bowel disease. It has even been shown to induce remission. But little is known about the bacterial species and metabolic pathways associated with treatment response – in other words, researchers don’t quite know what works, and what doesn’t.

In this study – published today in the prestigious journal Gastroenterology – the team analysed faecal and colonic samples from participants of the FOCUS clinical trial to identify bacteria signatures that result in a positive therapy outcome. Half the participants were given placebos.

“The most important aspect of this study – and why it’s so exciting – is that we are starting to figure out which bacterial species and functional pathways are ‘good’ and which are ‘bad’ when it comes to FMT for UC,” says Dr Nadeem Kaakoush, senior author from UNSW Medicine.

“Importantly, this is a study in humans, rather than animal models, so the results are very translatable.”

The scientists found that remission was associated with Eubacterium and Roseburia species, short-chain fatty acid biosynthesis, and secondary bile acids. Lack of remission was linked to Fusobacterium, Sutterella, and Escherichia species and increases in heme.

Poo transplants involve transferring poo from a healthy donor to a sick recipient. The collective community of bugs and compounds (the gut microbiota) in the donor’s poo is then believed to establish itself in the recipient’s gut.

The screened donor poo is delivered to the recipient in a number of ways, ranging from recipients swallowing a poo capsule (or “crapsule”) containing frozen poo, to a diluted sample being delivered through a plastic tube inserted into the nose down to the stomach or small bowel (nasogastric intubation).

The scientific consensus is that poo transplants work if the recipient’s gut microbiota is “restored”. The most consistent measure of this has been an increase in the diversity of the community of organisms in the recipient’s gut – the idea is that this community allows the recipient to resist being overwhelmed by the “bad” bugs.

The team hope that their findings will inform how FMT donors are selected, and how lab-grown mixtures are developed down the line. 

“We need further studies in patients and animal models of colitis to confirm that these microbes and products are associated with the efficacy of FMT,” Dr Kaakoush says.

“In our study we generated quite a large amount of data that will be mined and analysed for quite some time. This will allow us to develop further insights into FMT.

“This is a milestone in what will be a longer process of developing microbial mixtures that are effective at inducing remission. Many of these microbial based therapies will end up being individualised down the line as what works for one patient might be a little different from what works in other patients. Of particular importance at this early stage is figuring out what is good and what is bad, first,” he says.

You can learn more about how poo transplants work in this Conversation article by some of the study’s authors.