Silver makes bacteria more susceptible to antibiotics; new finding could help researchers develop better cures in the future.
Treating bacteria with a silver-containing compound boosted the success of some commonly used antibiotics, according to a Wyss Institute for Biologically Inspired Engineering at Harvard University press release.
Silver was a common treatment for infections before penicillin was invented in the 1940s. Antibiotic-resistant bacteria have been a growing problem over the past few years, and scientists have had a hard time finding stronger cures. Now they are turning to older methods.
The researchers observed the silver-treated antibiotics quickly stopped lethal infections in mice, and were even effective in some normally antibiotic-resistant bacteria. The team discovered silver made the bacteria between 10 and 1000 times more sensitive to ampicillin, gentamycin, and ofloxacin, three popular antibiotics.
Silver allowed an antibiotic called vancomycin, usually only effective in killing a type of pathogen known as Gram-positive bacteria, to kill Gram-negative bacteria. These bacteria can cause illnesses such as food poisoning and dangerous infections normally spread throughout hospitals.
The treatments were also effective against bacteria that often lie dormant during the first round of antibiotics, causing patients to undergo multiple courses of treatment. The silver treatments, in combination with vancomycin, saved the lives of 90 percent of the mice afflicted with peritonitis, an infection in the area around the internal organs. Only 10 percent of the mice treated with only antibiotics survived.
"The results suggest that silver could be incredibly valuable as an adjunct to existing antibiotic treatments," Jim Collins, Ph.D, of the Wyss Institute and Boston University said.
Despite the use of silver to treat infection over the course of history, scientists knew very little about why it worked. Ruben Morones-Ramirez, Ph.D., a postdoctoral fellow at the Wyss Institute who recently became a professor at the Universidad Autònoma de Nuevo Leon in Mexico used silver to treat common and mutant strains of E Coli.
He noticed the silver-treated bacteria produced more reactive oxygen species, which are chemically reactive molecules which can damage the bacteria cell's membrane, DNA, and enzymes. Silver was once used as a cure by itself, but the researchers believe it could be used in combination with antibiotics to make the bacteria more susceptible to the treatment.
"If you know the mechanism, you can have much more success making combinatorial therapies," Morones-Ramirez said.
Toxicity screenings showed the amount of silver needed to affect the bacteria was well below a dose that could cause harm to the mice, it also proved not to be harmful in cultures of human cells.
"Doctors desperately need new strategies to fight antibiotic-resistant infections, and Jim and his team have uncovered one that's incredibly versatile, and that could be put to use quickly in humans," Don Ingber, M.D., Ph.D., the Wyss Institute Founding Director said.
