July 29, 2008 -- It's a Godzilla vs. King Kong match-up -- in mice.

Researchers have pitted the food-poisoning bug salmonella against breast, colon, and skin cancers in lab animals. Who wins?

Hint: Don't bet on the cancer.

Markus Loeffler, MD, John C. Reed, MD, PhD, and colleagues at California's Burnham Institute for Medical Research took advantage of the fact that salmonella bacteria home in on cancer cells and accumulate in tumors. But for medical use, the bacteria have to be rendered harmless. What chance would they have against cancer cells?

To fix the odds in salmonella's favor, Loeffler and colleagues turned the bugs into ticking time bombs. They genetically engineered the bacteria to give off the FasL cytokine, a deadly chemical signal that tells cells to commit suicide and also attracts attack by immune cells.

When injected into mice with breast or colon cancers, the salmonella did exactly what they were supposed to do. They inhibited the growth of breast tumors by 59% and growth of colon tumors by 82%. Moreover, they reduced the tumor spread to other parts of the body by a third.

Perhaps most importantly, the deadly chemical signal the bacteria carried did not damage the mice.

The results, Loeffler and colleagues conclude, suggest that genetically engineered salmonella "could offer an acceptable strategy for employing FasL and possibly other toxic cytokines for cancer therapy."

The researchers report their findings in the Aug. 6 issue of the Journal of the National Cancer Institute.