People often think of E. Coli poisoning as a beef-eater's disease, but the outbreak linked to raw spinach is a tragic reminder that the bacteria often spread through animal droppings into produce growers' water, soil or fertilizer. Microbiologists Andrew Brabban and Betty Kutter want to kill the nasty bug at its source, in the intestines of livestock, using a virus that's a natural enemy of E. coli.

The researchers at Washington's Evergreen State College discovered it when their students were studying E. Coli in sheep at the USDA Food and Feed Safety Research Unit. "Every time they tried to infect the sheep with E. Coli, the sheep seemed to be within two days perfectly happy and they couldn't find the bacteria," says Brabban. "They had some natural resistance."

It turned out that the resistant sheep harbored a virus called a bacteriophage, or simply phage, that specifically preys on E. Coli bacteria. "A phage is a virus that specifically infects a bacterium so it can't infect people and it can't infect animals and it can't infect plants. And not only that, but each phage attacks particular kinds of bacteria," Kutter explains. A phage attacks its host bacterium by injecting its DNA into the bacteria cell. New phages multiply inside and eventually burst through the bacterium, killing it.

As they report in the journal Applied and Environmental Microbiology, the phage they isolated from the sheep, called CEV-1, kills many strains of disease-causing E. Coli in laboratory cultures.

Their goal is to develop a phage cocktail that works reliably when fed to livestock. "We'd simply give it to them in their food or in their drinking water," says Brabban. That may take years of research.

But since the phage works so well outside the animals, Brabbab says it may be possible to develop it as a mist or spray to treat produce before it can be used to treat animals. In August, the Food and Drug Administration (FDA) approved the first-ever phage treatment to kill a different bacteria—listeria—on foods. Brabban says that because it takes so few E. Coli bacteria to cause disease, the challenge is to make sure any treatment kills all the E. Coli, whether in animals or on fresh foods.

The research is being funded by the National Institutes of Health and the US Department of Agriculture.