The gut infection Clostridium difficile can be defeated by a cocktail of rival good bacteria, experiments in mice show.
When C. difficile bacteria overwhelm the gut, it can be fatal and difficult to treat with antibiotics.
A UK team showed a combination of six bacteria could clear the infection.
The study, published in PLoS Pathogens, builds on faecal transplant procedures - which are used to introduce competing bacteria.
C. difficile bacteria live in many people's guts alongside hundreds of other species - all fighting for space and food.
However, a strong course of antibiotics can kill off C. difficile's competition. Numbers then explode, C. difficile dominates the gut and masses of toxins are produced. It results in diarrhoea and can be deadly.
The main treatment, antibiotics, is part of the problem. It means the condition can be difficult to get rid of and can affect patients again and again.
Rarely, some patients have faecal transplants as a way of restoring the balance of bacteria in the gut. Material is taken from a donor, mixed with water, filtered and passed down a tube into the stomach. It is thought to be successful in about 90% of cases.
However, even the only doctor in the UK to use the treatment, Dr Alisdair MacConnachie from the Gartnavel General Hospital in Glasgow, says it's a last resort and quite frankly "disgusting".
'A tough bug'
In this latest study, researchers at the Sanger Institute, near Cambridge, tried to find exactly which bacteria in faecal transplants were needed to clear the infection.
They grew bacteria from mouse faeces in the laboratory and tried different combinations of bacteria in infected mice.
They found a combination of six, including three previously unidentified species, did the trick.
The super-six cocktail cleared the infection in all 20 infected mice given the oral treatment. Crucially the bacteria can be grown in the lab without needing a fresh sample for each transplant.
The scientists said the procedure shifted gut bacteria to a healthy state.
One of the researchers involved, Dr Trevor Lawley, said: "It is quite intuitive to aim for more balanced gut ecosystems.
"Antibiotics are the greatest medical invention ever, but maybe we've overused them and C. diff is the result.
"It's a very very tough bug to deal with."
He said there were differences between the bacteria growing in the guts of mice and people, so the same experiments now needed to be repeated to find an equivalent cocktail for people.
Neil Fairweather, professor of microbiology at Imperial College London, said faecal transplants had problems, such as the risk of transferring harmful infections.
But he said he could see treatments using just the bacteria being used in the future.
"There is the obvious benefit of not having to prepare an emulsion of human poo prior to transplantation - growing bugs in culture is far preferable and less smelly!
"One can imagine patients being offered a pill containing a number of defined bacterial species that will help restore the normal mix of 'healthy bacteria' in the gut.
"Other conditions that have been associated with imbalance of the gut microbiota include inflammatory bowel disease and it is possible that bacteriotherapy could have promise in such conditions."
Dr Anton Emmanuel, from the British Society of Gastroenterology, said this was exciting research.
"What we do know is that faeces contain several million bacteria, however, some of which may be beneficial to health but some may be harmful.
"Screening to find what are the good components is part of the holy grail of this type of therapy."