Silver can make antibiotics more effective

LONDON: Tiny amounts of silver added to antibiotics could make them 10 to 1,000 times more effective and enable them to fight drug-resistant infections, a new study has claimed. 

Scientists at the 
Wyss Institute for Biologically Inspired Engineering at Harvard University found treating bacteria with a silver-containing compound boosted the efficacy of a broad range of widely used antibiotics and helped them stop otherwise lethal infections in mice. 

It also helped make an antibiotic-resistant strain of bacteria sensitive to antibiotics again. And it expanded the power of an antibiotic called vancomycin that is usually only effective in killing pathogens called Gram-positive bacteria, such as Staph and Strep. 

Silver allowed vancomycin for the first time to penetrate and kill Gram-negative bacteria, a group that includes microbes that can cause food poisoning and dangerous hospital-acquired infections. 

Silver also proved useful for two types of stubborn infections that usually require repeated rounds of antibiotic treatment and multiple visits to the clinic: dormant bacteria that lie low during antibiotic treatment and rebound to cause recurrent infections, and microbial slime layers called biofilms that coat catheters and prosthetic joints. 

"The results suggest that silver could be incredibly valuable as an adjunct to existing antibiotic treatments," said 
Jim Collins, a pioneer of synthetic biology and Core Faculty member at the Wyss Institute. 

In the study, researcher 
Ruben Morones-Ramirez treated normal and mutant strains of E colibacteria with a silver compound. Then he observed them under the electron microscope and ran a series of biochemical tests. 

He found that silver compounds cause bacteria to produce more reactive oxygen species - chemically reactive molecules that damage the bacterial cell's DNA and enzymes, as well as the membrane that encloses the cell. 

The results showed that a small amount of silver made E coli bacteria between 10 and 1000 times more sensitive to three commonly used antibiotics: gentamycin, ofloxacin, and ampicillin. 

In mice, silver also helped antibiotics fight E coli-induced urinary-tract infections. It made a previously impervious strain of E coli sensitive to the antibiotic tetracycline. 

It allowed vancomycin to save the lives of 90 per cent of mice with life-threatening cases of peritonitis - inflammation caused by infections of the abdominal space surrounding the internal organs. Without silver, only 10 per cent of the mice survived. 

The scientists also found that the doses of silver needed to help antibiotics did not harm cultured human cells, suggesting that oral and injectable silver could be safe for humans as well. 

The study was published in Science Translational Medicine.