The bacteria that cause food poisoning could be used to kill cancer, medical experts said yesterday.
A genetically-altered form of salmonella has been developed that will attack tumour cells but leave healthy cells alone.
The bugs are a leading cause of food poisoning in the UK each year.
It is the latest example of developments in a new field of cancer treatment called "bacteriotherapy".
Experiments on mice using a modified version of salmonella reduced the size of cancer tumours, the American Association for the Advancement of Science annual meeting in Boston heard.
It was also engineered to create "flags" that are recognised by the immune system, guiding the body's defence system to target the cancerous tumours.Alterations made to the salmonella bug stopped it attacking and infiltrating into normal healthy cells. Instead it targeted cancer cells.
When injected into the bloodstream of mice with colon cancer, tumours exposed to the bacteria shrunk.
The development, led by Jin Hai Zheng from Chonnam University in South Korea and colleagues, was published in the AAAS journal Science Translational Medicine.
Dr Zheng said: "The engineered bacteria induced an effective antitumor immune response, successfully treating tumours in several different mouse models with no evidence of toxicity."
The breakthrough was hailed by British researchers yesterday.
Kevin Harrington, professor of biological cancer therapies at the Institute of Cancer Research in London, said: "It has been known for some time that certain types of bacteria, including strains of salmonella, are able to grow in tumours but not in normal tissues.
"However, until now, attempts to use bacteria as anti-cancer therapies have had limited success, both in the laboratory and in the clinic.
"The current work by Zheng and colleagues represents a fascinating new approach to using bacteria.
"Instead of asking the bacteria to kill cancer cells directly, the researchers have genetically engineered salmonella so that it expresses a gene from a different bacterium and this triggers the immune system to mount an attack on the tumour.
"The results show that this approach is effective against a range of tumour types with little or no toxicity in mice."
Dr Catherine Pickworth, Cancer Research UK's science information officer, added: "In this study the researchers injected the bacteria into the mice where it was delivered to the tumour through the blood, causing an immune reaction.
"The bacteria fits like a lego piece onto the surface of immune cells. This starts a chain reaction inside the immune cells, causing them to release molecules that can kill cancer."
Dr Pickworth went on: 'This study, carried out in mice, shows that bacteria can be used to trigger the immune system to attack cancer cells. The next steps will be to see if this method is safe and if it could be used to help patients.
"We're funding similar research using viruses to help the immune system recognise cancer cells as a threat so it can destroy them, opening potential new ways to treat the disease."
Professor Paul Dyson, of Swansea University, who is also studying the use of salmonella in fighting cancer said one advantage is that "the salmonella are living factories for production of therapeutic molecules.
He added: "So long as the tumor persists, potentially the bacteria will continuously produce the therapeutic agents.
"So we believe there is huge mileage in pursuing research into this type of treatment. Existing evidence indicates there would few or no side effects."
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