Silver fights drug-resistant infections
Silver has long been known for its anti-bacterial properties. Now it could be used to fight antibiotic-resistant "super-bugs". James Mitchell Crow reports.
An ancient antimicrobial treatment could soon help doctors solve a very modern health problem. Silver’s infection-fighting abilities have been recognised since at least 400 BC, when Hippocrates was using it to help wounds heal faster. James Collins at the Howard Hughes Medical Institute in Boston, US, and colleagues have now shown that silver can help overcome modern drug-resistant bacteria, including certain antibiotic-resistant E. coli strains.
The researchers made their discovery while investigating just how silver exerts its effects. Despite centuries of use, silver’s microbe-killing mode of action was still unclear, says Jose Ruben Morones-Ramirez, a member of Collins’ team. The team found that silver ions tip the bacteria’s cellular chemistry out of balance, killing the cells by generating deadly levels of highly destructive molecules called reactive oxygen species (ROS). The ions also degrade the bacteria’s outer membrane.
As some antibiotics also kill bacteria through ROS generation, the researchers decided to test whether teaming these drugs with silver ions would create a more powerful medicine. The results were dramatic. The two treatments worked synergistically, the combination therapy up to 10,000 times more powerful than the antibiotic alone.
“When you combine two medicines you might get about a double or triple synergistic effect, so it was a pretty amazing result,” Morones-Ramirez says. In mice at least, the silver doses were well-tolerated by the animals’ own cells.
Back in ancient Greece, Hippocrates had also noted silver’s ability to purify water – a challenge in many developing nations today. Silver might sound like a costly answer, but Thalappil Pradeep and his co-workers at the Indian Institute of Technology Madras, in Chennai, has developed a robust composite water filter that leaks purifying silver ions at such a slow rate that the treatment should cost US$2.50 per family per year. The level of silver in the filtered water was well below the limit considered dangerous by the US Environmental Protection Agency, yet cleaned the water of bacteria and viruses.