Tuesday, April 15, 2008

Using Viruses to Kill Bacteria

In the fight against infection, viruses may take up where antibiotics leave off.

By Jennifer Chu

In stitches: Hospital sutures coated with a bacteria-fighting virus (shown above) effectively killed off 96 percent of an antibiotic-resistant bacteria in culture. Researchers used these same sutures to sew up bacterially infected wounds in live rats. The treated stitches prevented infection from flaring up, while rats with untreated sutures developed large sores and inflammation. Credit: University of Strathclyde

Hospitals are fertile ground for infectious bacteria, which can spread rapidly across countertops, stethoscopes, and catheters. These "superbugs" infect up to 1.2 million patients a year in the United States, according to a 2007 report from the Association for Professionals in Infection Control and Epidemiology, and they're quick to evolve defenses against even the most powerful antibiotics.

Now scientists in Scotland have come up with an alternative to antibiotics, which may effectively stop bacteria in its tracks. Janice Spencer and a team of researchers at the University of Strathclyde are developing nylon sutures coated with bacteriophages--viruses, found naturally in water, that eat bacteria while leaving human cells intact. New research by the Scottish team found that phage-coated sutures effectively stemmed infection in live rats.

Bacteriophages are not a recent discovery. During World War II, Russian doctors used cocktails of these viruses to treat soldiers infected with bacteria such as dysentery and gangrene. However, researchers soon turned their attention from bacteriophages to the rapidly rising field of antibiotics, developing new classes of antibiotics to combat ever-more-resistant strains of bacteria.

"Now we're coming to the end of the usefulness of antibiotics," says Spencer. "It takes time to get new classes of antibiotics onto the market, whereas bacteriophages can be easily isolated from environmental sources such as sewage water."

In water, these natural-born killers are extremely effective at eating up bacteria. The virus binds to bacteria and injects its DNA, replicating within its host until it reaches capacity, whereupon it bursts out, killing the bacteria in the process.

Obtaining bacteriophage-laden water samples is easy, says Spencer. The challenge is in keeping virus molecules active out of water. In dry environments, the virus's proteins tend to fall apart in a matter of hours, rendering them ineffective against bacteria. Spencer and her colleagues isolated bacteriophages from water samples and developed a novel method to keep them active.

The team chemically bound bacteriophages to microscopic polymer beads by first breaking the surface of the polymer. Then the researchers added a linker molecule to the polymer's surface, which in turn binds to bacteriophages and keeps them from falling apart. To test the virus's virulence, the team first made small incisions in live rats, then infected them with Methicillin-Resistant Staphylococcus Aureus (MRSA), one of the most resistant strains of bacteria found in hospitals. Half of the rats were stitched up with sutures that were coated with polymer-bound bacteriophages. The other rats were closed up with untreated sutures.

Spencer and her colleagues found that the wounds dressed with the treated sutures appeared to have no infection, while those stitched with regular sutures became inflamed, with large sores and "abundant pus."