A novel use has been found for the biotechnologist's ubiquitous laboratory tool—the bacteriophage. Bacteriophages naturally infect and kill bacteria, but researchers have now identified a deadly bacteriophage extract that can kill bacteria on contact (Proc. Natl. Acad. Sci. 98, 4107–4112, 2001). Researchers from the Rockefeller University (New York) extracted the enzyme, lysin, from bacteriophage specific to group A streptococci—the cause of “strep” throat, rheumatic fever, and also “flesh-eating” infections. When lysin was given orally and nasally to mice infected with group A streptococci, it eradicated the pathogen by punching holes in its cell walls. The surrounding microflora were largely unaffected. Although further studies are needed to ensure that bioactive bacterial cell wall fragments are not released systemically, bacteriophage enzymes could be a novel means of preventing infections by clearing reservoirs of potentially pathogenic bacteria from human mucous membranes. Because the enzyme kills on contact, it avoids the potential risk of antibiotic resistance. Vincent Fischetti, senior author on the paper, says the team will next engineer a single bacteriophage enzyme to target several pathogenic bacteria.