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Faecal transplants work best when stool samples are given by ‘super donors’

Faecal microbial transplants (FMT) work best when stool samples are taken from ‘super donors’, research suggests.

A study investigating the effectiveness of FMTs in a range of diseases found the nauseating procedure is most successful when excrement is transplanted from those with high levels – and a rich diversity – of ‘good bacteria’ in their guts.

The researchers hope identifying super donors will help scientists understand what makes their samples so effective.

And they hope it could lead to trials of the grim procedure for other conditions linked to an imbalance of gut bacteria, including Alzheimer’s, multiple sclerosis and asthma.

But, the scientists add, there is likely no ‘one size fits all’ approach, with FMT success depending on the gut’s overall bacterial make-up, as well as how the bugs interact with each other and the recipient’s immunity.  

Faecal microbial transplants (FMT) work best when stool samples are taken from ‘super donors’, research suggests. FMTs have been shown to have up to 92 per cent efficacy in treating recurrent C.diff infections but are less effective in other gut conditions (stock)

The study was carried out by the University of Auckland and led by Brooke Wilson, a research assistant in the department of philosophy. 

Poor bacteria diversity in the gut has been associated with everything from asthma and irritable bowel syndrome (IBS) to obesity and heart disease, the researchers wrote in the journal Frontiers in Cellular and Infection Microbiology. 

FMT aims to boost a recipient’s gut bacteria levels and diversity by taking purified stool samples from a healthy donor.

The procedure has shown to be successful in up to 92 per cent of cases of recurrent C.difficile infections that do not respond to antibiotics. 

C.diff is usually suppressed by a healthy gut but if the microbiome’s diversity is reduced – such as after taking antibiotics – the pathogen can multiply, leading to inflammation of the intestines and subsequent diarrhoea. 

But FMT’s effectiveness in other conditions that cause a change to the gut’s bacterial make-up – such as constipation, IBS and liver disease – have a much more varied patient response. 

To better understand the super-donor phenomenon, the researchers reviewed numerous faecal transplant trials to uncover what makes these donors unique.

And they discovered super donors have a richer amount of bacteria in their stools.

Senior author Dr Justin O’Sullivan, associate professor of microbiology, said: ‘It is well-known that responders typically exhibit a higher microbial diversity than non-responders. 

‘In line with these observations, a larger number of species in the donor stool has been shown to be one of the most significant factors influencing faecal transplantation outcome.’

Super donors also have higher amounts of so-called ‘keystone bacteria’, which produce chemicals that are notably lacking in diseased guts.

‘In inflammatory bowel disease and diabetes for example, keystone species that are associated with prolonged clinical remission produce butyrate,’ Dr O’Sullivan said.

‘[This is a] chemical with specialised functions in regulating the immune system and energy metabolism.’ 

These keystone bacteria could be tested for their efficacy by selecting donor stools rich in particular strains. 

‘Precision’ transplants with a set mix of beneficial bacteria could also be created to see how effective they are.

‘This approach has been applied successfully to prevent complications in a small sample of patients with liver disease,’ Dr O’Sullivan said. 

‘However, this study showed that microbial enrichment in the donor does not completely guarantee enrichment in the recipient.’

There is likely more to donor-recipient success than just keystone species, with the balance of bacteria overall and the interactions between the bugs probably also playing a role. 

‘For example, the success of faecal transplants has been associated in some studies with the transfer of viruses which infect other gut microbes,’ Dr O’Sullivan said.

‘Some cases of recurrent diarrheal infection have even been cured with transplants of filtered stool, that has had all the live bacteria filtered out but still contains DNA, viruses and other debris.

‘These viruses could affect the survival and metabolic function of transplanted bacteria and other microbes.’

Super donors likely only work if the recipient has the right bacterial make-up, which can change quickly depending on their diet. 

‘Some faecal transplant failures may be attributable to the gut’s immune response to transplanted microbes, possibly stemming from an underlying genetic difference between the donor and the recipient,’ Dr O’Sullivan said

‘Supporting the transplanted microbiome through diet could also improve success. 

‘It has been shown that a rapid change in diet, such as a switch from an animal-based to an exclusively plant-based diet, can alter the composition of the gut microbiota within 24 hours.’

A person’s diet provides the fuel for anti-inflammatory bacteria to survive and multiply, driving out ‘bad bugs’. 

The researchers recommend future FMT studies record the recipients’ genetic make-up and diet to understand which transplants work best. 


Faecal microbiota transplantation (FMT) is the transfer of stool from a healthy donor into the gastrointestinal tract of a patient.


It is most commonly used to treat recurring C. difficile infection – spread by bacterial spores found within faeces. It is 90 per cent effective.

It can also be used to treat gastrointestinal conditions such as colitis, irritable bowel syndrome and constipation – but success rates are much lower. 

Recent studies have delved into the benefits of treating conditions linked to a poor balance of ‘good’ and ‘bad’ bacteria in the gut, such as autism. 

Faecal microbiota transplantation (FMT) is the transfer of stool from a healthy donor into the gastrointestinal tract of a patient

Faecal microbiota transplantation (FMT) is the transfer of stool from a healthy donor into the gastrointestinal tract of a patient

FMT can replenish bacterial balance as it acts like a probiotic, with samples of faeces often containing up to 1,000 different species of bacteria.  


The transplant is done via tubes – inserted into the nostril, down the throat and into the stomach – or directly into the colon.

However, the faecal sample can also be transplanted through enemas or pills containing freeze-dried material.


There have been reports of patients showing unexpected weight gain after treatment, bouts of vomiting and even abdominal pain.

However, the long-term safety and effectiveness of FMT is relatively unknown, and researchers have called for more studies to determine the risks.