Increasingly many bacteria are becoming resistant to antibiotic treatment, presenting a serious public health threat. But new research reveals that these bacteria are often still vulnerable to natural enemies from withinnamely an enzyme manufactured by viruses, or bacteriophages, found inside the organisms. "These enzymes offer an alternative method for combating resistant pathogens," says Rockefeller University's Vincent Fischetti, lead investigator on the work described in today's issue of Science. "A nasal spray containing this enzyme would prevent infections before they start. We would no longer have to wait for an infection to arise in order to treat it."

Unlike traditional antibiotics, which attack bacteria that have already infected some cell, the enzymes do battle with bugs on the surface of mucous membranes. When bacteriophages produce the compound inside bacteria, it punches holes in the organisms' cell walls, leading to their death. Fischetti and colleagues discovered that it had the same effect when applied from the outside. The team eliminated Streptococcus pneumoniae on the membranes between the back of the nose and throat in mice and showed that the enzyme could also kill penicillin-resistant strains of the pathogen in a test tube.

"This enzyme will kill pneumococci on mucous membranes within seconds," co-author Jutta Loeffler says. "By treating individuals carrying this bacterium with the enzyme, you could significantly reduce the reservoir of these bugs in the population and consequently reduce infection rates." The Centers for Disease Control and Prevention (CDC) ranks S. pneumoniae among the leading causes of illness and death in young children, those in poor heath and the elderly worldwide.

The enzyme therapy offers several significant advantages. It can be tailor-made for any bacterium, Fischetti notes, and thus should produce fewer side effects than antibiotics, which kill both good and bad bacteria in the body. In addition, it is unlikely to lead to resistance. The only downside is that the enzyme will probably not cure full-blown infections and so must be used on occasion in conjunction with antibiotics. Clinical trials are now in the planning stages