London, Thu Jun 20 2013
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 coli bacteria 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.
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