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A CLOSER LOOK: ANTI-LISTERIA SPRAY

Latest food additive: Viruses

The FDA-approved bacteria eaters work on deli meats and other ready-to-eat foods.

August 28, 2006|Hilary E. MacGregor | Times Staff Writer

If you want to get rid of a pest, why not use a littler pest to plague it? That's the tack OKd last week by the Food and Drug Administration, which has for the first time approved the use of bacteria-eating viruses as an additive to foods.

From now on, these viruses -- known as bacteriophage or phage -- can be sprayed on ready-to-eat cold cuts and luncheon meats by manufacturers to prevent listeriosis, the most deadly of all food-borne illnesses in this country.

The premise: Should listeria bacteria be lurking in your bologna or smoked turkey slice, the phage will attach to them, enter them and kill them.

To the average consumer, the notion that companies might spray live viruses on meat to protect people from disease seems counterintuitive, if not downright weird. But phage experts say there is nothing to fear.

"They are very safe," said Vincent Fischetti, a professor of microbiology at Rockefeller University in New York, and the head of the lab of bacterial pathogenesis. "These viruses do not affect humans. They only infect bacteria.

"It's just scary because everybody says stay away from viruses, and now we are eating them."

The FDA spent four years evaluating the safety and effectiveness of the "cocktail" of several phage at the request of Intralytix Inc., a Baltimore, Md., biotechnology company. In presenting its petition, Intralytix referred the government to more than 20 studies documenting the power of phage to fight infection, many of them performed in Russian and Eastern Bloc countries where phage therapies have long been popular in treating certain infections.

Intralytix also conducted studies of its own, trying out its phage mixture (consisting of six different phage that attack the food-poisoning bacterium Listeria monocytogenes) on more than 10 different kinds of deli meats, including sliced turkey, roast beef, bologna, chicken and even raw hot dogs, and found that they effectively killed all strains of listeria.

Phage are everywhere -- in the water, soil and our intestines and mucus membranes. Phage experts are fond of saying they're the most abundant life form on Earth. They are far tinier than bacteria: If you stacked every one of them end to end, you would have to travel at the speed of light for 200 light years to get to the top of the stack, said Fischetti, who is a consultant to a biopharmaceutical company exploring the use of phage in treating anthrax. About 10 million commonly reside in a single milliliter of unpolluted water, he said.

Phage were discovered in Paris about a hundred years ago, and, with their discovery, scientists believed they had discovered the key to controlling bacteria. When antibiotics were later discovered, phage research was abandoned in the West. But in the Soviet Union, the research flourished and institutes were devoted to developing phage therapies.

Certain cities still hold huge collections of bacteriophage and when antibiotics fail, Russian patients are often still sent for doses of phage.

As the medical problem of antibiotic resistance has grown, some Western researchers are revisiting phage as an alternative -- or supplement -- to conventional bacteria-fighting therapies.

Phage act by infiltrating disease-causing microbes and destroying them from within, effectively turning their prey into phage-producing factories. A single phage particle, once it invades, will produce 50 to 100 more phage that emerge and invade more bacteria.

But harnessing these tiny viruses to fight food poisoning takes more than just spraying cold cuts with random collections of phage. Invading phage and enemy bacteria must be perfectly matched for the process to work. Each strain of phage is highly specific and kills only certain bacteria.

Also, bacteria become resistant to certain strains of bacteriophage very rapidly. That is why, in this new spray-on application for ready-to-eat meats, Intralytix scientists are using six different phage. To come up with their cocktail, the scientists collected more than 300 different strains of listeria and tested listeria-invading phage on all of them. There was no single phage that killed all strains, so the scientists designed the product so that every kind of listeria would be attacked by more than one phage.

In other words, "there is lots of protection in case a mutation occurred," said John Vazzana, president and chief executive of Intralytix.

According to the Centers for Disease Control and Prevention, each year 2,500 people in the United States become sick from listeriosis, and about 500 die. Those usually affected are pregnant women, newborns and adults with weak immune systems.

The bacteriophage additive was approved for use on ready-to-eat meats, which are normally consumed without additional cooking, said Andrew Zajac, acting director of the division of petition review in the FDA Office of Food Additive Safety.

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