Aussie researchers have worked out a way to identify ideal poo donors in a promising breakthrough that should help people with chronic gut disease.

Researchers have finally identified which bacteria are good and which are bad when it comes to poo transplants that can help sufferers of ulcerative colitis.

It's been known for some time that faecal transplants are an effective treatment for the disease, which causes inflammation of the lining of the bowel wall.

Transplants involve taking faecal matter from healthy donors and putting it in the digestive tracts of patients, either via a nasal tube or a capsule of frozen poo that can be swallowed.

Once inside the patient's body, good bacteria from the donor can take hold and establish a healthy community capable of putting ulcerative colitis into remission.

But what hasn't been known until now is which specific bacteria are best at easing symptoms of disease, and which ones are ineffective.

New research led by researchers at the University of NSW has finally started to clear that up and that's a big leap forward, the study's senior author says.

"We are starting to figure out which bacterial species and functional path ways are good and which are bad when it comes to faecal microbiota transplantation for ulcerative colitis," Dr Nadeem Kaakoush said.

Scientists found remission was associated with Eubacterium and Roseburia species, short-chain fatty acid biosynthesis, and secondary bile acids.

A lack of remission was linked to Fusobacterium, Sutterella, and Escherichia species.

Dr Kaakoush and his team say their findings will inform how poo donors are selected, and how lab-grown mixtures are developed in the future.

"This is a milestone in what will be a longer process of developing microbial mixtures that are effective at inducing remission," he says.

"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."

The UNSW study was carried out in collaboration with other researchers in Australia and the United States, and has been published in the journal Gastroenterology.