The FDA has approved a spray-on mixture of bacteria-killing viruses as additives to cold cuts, wieners and sausages to destroy Listeria microbes, which kill hundreds of people in the US each year.

The Food and Drug Administration on Friday declared the virus mix safe to spray on such foods as cold cuts, hot dogs, sausages, sliced ham and turkey prior to packaging.

Foods like these are especially vulnerable to Listeria because they are often not reheated prior to consumption, explained Andrew Zajac of the FDA's Office of Food Additive Safety. Cooking meat kills the Listeria bacterium, but foods can become contaminated after processing.

The FDA's approval of the mixture -- the first time viruses have been approved for use as a food additive -- is a "huge milestone" in the fight against food-borne illnesses, said John Vazzana, chief executive officer of Intralytix. Pregnant women, newborns and adults with weakened immune systems are especially vulnerable to listeriosis. The Centers for Disease Control and Prevention has estimated that 2,500 people become seriously ill with the infection each year, and 500 ultimately die from it.

Bacteriaphages are grown in a preparation of the same bacteria they are designed to kill, and then purified.

According to Intralytix, typical phages have hollow heads that store their viral DNA and tunnel tails with tips that bind to specific molecules on the surface of their target bacteria. The viral DNA is injected through the tail into the host cell, where it directs the production of progeny phages.

These "young" phages burst from the host cell, thereby destroying it, and go on to infect more bacteria. The viruses will not kill any organism other than their target bacteria.

Prior to issuing its approval, the FDA was concerned that the virus preparation might contain toxic residues associated with the bacteria. Tests found no residues present, however. In small quantities, such residues would be unlikely to cause any health problems, the FDA said.