Sara Bartels and Siegfried Weiss, of the Helmholtz Centre for Infection Research (HZI) in Braunschweig, say that a messenger substance from the immune system makes blood vessels in the cancerous tissue permeable, and thereby enables the bacteria to conquer and destroy the tumour.
The researchers add that, simultaneously, blood streams from the vessels into the cancerous tissue, a so-called necrosis develops, and the tumour dies.
"This influx of blood was the starting point for our investigations. There is an immunological messenger present during bacterial elicited inflammation that causes this kind of reaction. We searched for it - and found it," says Siegfried Weiss, Head of the Molecular Immunology group at the HZI.
The researchers have revealed that this messenger is named after its role in the immune system: tumour necrosis factor, TNF-alpha for short.
They say that immune cells produce TNF-alpha when recognising salmonella, thus alarming other immune cells.
According to them, a small amount of TNF-alpha is subsequently enough to dissolve the walls of the blood vessels in the tumour and allow the blood to stream into the cancerous tissue.
They hope to be able to modify salmonella so that they can migrate specifically into tumours and cause them to die.
Since salmonella can live even in tissues that are badly supplied with blood, the researchers believe that they can be used in tumour therapy.
This is interesting because chemotherapeutics cannot be transported to an area where there is no blood flow, and even radiation therapy requires oxygen for its reactions in the tissue.
"We have obtained an important indication of how bacteria migrate into tumours. We can now try to manipulate these bacteria to use them in cancer therapy without causing deadly infections," says Sara Bartels.
"We need to find the right amount of bacteria aggressiveness, allowing the tumour to be colonised and destroyed without harming the patient," she adds.
If the scientists succeed in accomplishing this feat, they may be able to take the next step forward: using salmonella to release therapeutic substances within the tumour and thus participate in its destruction.
"Our experiments are currently limited to absolutely basic research and experiments with laboratory mice. It may take years before this method is usable for human patients," says Siegfried Weiss
The study has been published in the scientific journal PLoS ONE.