In The Economist, some new ideas about silver:
Silver has long been known as more than bling. In the fifth century BC Hippocrates noted its ability to preserve food and water. In the late 19th century silver-nitrate eye drops were administered to newborns to prevent conjunctivitis (though this remedy has since been replaced with an antibiotic). Today silver is routinely found in wound dressings and catheters to treat or prevent infections. Yet, despite its widespread use, the source of silver’s antibacterial properties has remained shrouded in mystery.
Now Jose Morones-Ramirez, from Boston University, and colleagues think they may have cracked it. As they report in Science Translational Medicine, silver fights bacteria in a number of ways.
First, silver ions (as atoms stripped of some of their electrons are known) help, through a process known as the Fenton reaction, to convert hydrogen peroxide into molecules called hydroxyl radicals. Radicals are unstable and readily react with cellular components, damaging them. Indeed, an excess is thought to contribute to ageing-related illnesses in humans. However, the researchers found, concentrations of silver ions low enough to leave human cells unscathed nonetheless appear to wreak havoc on bacterial ones.
Using a dye that glows in the presence of hydroxyl radical, Dr Morones-Ramirez treated the bacterium Escherichia coli with silver nitrate (a source of silver ions). The E. coli glowed, and then promptly bit the dust. But when the bacteria were first bathed in a chemical which mops up the hydroxyl radicals, they survived. This points to silver’s effect on the production of hydroxide radicals as the explanation.
