SINSULL, according to the article that the first Anonymous.GUEST pointed to, the special viruses called bacteriophages are meant to kill strains of the Listeria monocytogenes bacterium, the Food and Drug Administration said in declaring it safe to use on ready-to-eat meats prior to their packaging. The bacterium the viruses target can cause a serious infection called listeriosis, primarily in pregnant women, newborns and adults with weakened immune systems.