A mixture of six bacteria-killing viruses can be safely sprayed on meat and poultry to combat common microbes that **** hundreds of people a year, federal health officials said Friday. The mixture of special viruses, called bacteriophages, would target strains of Listeria monocytogenes, the Food and Drug Administration said in declaring it is safe to use. The viruses are designed to be sprayed on ready-to-eat meat and poultry products just before they are packaged. The bacterium they target can cause a serious infection called listeriosis, primarily in pregnant women, newborns and adults with weakened immune systems. In the United States, an estimated 2,500 persons become seriously ill with listeriosis each year, according to the Centers for Disease Control and Prevention. Of those, 500 died. The preparation of bacteriophages — the name is Greek for "bacteria-eater" — infects only various strains of the Listeria bacterium and not human or plant cells, the F.D.A. said. People normally come into contact with phages through food, water and the environment, and they are found in our digestive tracts, the F.D.A. said. The viral preparation is made by Intralytix Inc. The Baltimore company first petitioned the F.D.A. in 2002 to allow the viruses to be used as a food additive.