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In a study published Wednesday in Science Translational Medicine, researchers found that by adding trace amounts of silver to common antibiotics, the medications became up to 1,000 times more effective in fighting infections in mice.
Also, study authors said they were surprised and excited to find that the silver-antibiotic combo was able to "re-sensitize" bacteria that had developed a resistance to the drugs. It even extended the effectiveness of the commonly used antibiotic vancomycin to a class of bacteria that was previously immune to its effects.
"We went from basically no killing to substantial killing," said senior author James Collins, a professor of microbiology at Boston University.
The study is one of the first comprehensive examinations of the ways that silver affects bacteria that are known as Gram-negative. These bacteria are equipped with an extra protective membrane that prevents antibiotic drug molecules from penetrating and killing them.
In a series of experiments, Collins and colleagues from Boston University and Harvard University examined the effects of a simple solution of silver nitrate salt on Gram-negative bacteria like Escherichia coli.
What they found was that even small amounts of silver ran roughshod over some of the toughest bacteria around.
"It did two things," Collins said. The positively charged silver ions degraded the bacteria's protective layer, giving the antibiotics easier access to the pathogens' innards. It also messed with the bugs' metabolism and their ability to manage their iron levels.
The second effect led to the creation of molecules that can kill bacteria, including oxygen molecules that are prone to chemical reactions that can damage cells, Collins said.
In one experiment, researchers induced peritonitis in mice by injecting them with E. coli cells. Of the mice treated with silver and vancomycin, 90% survived.
Mice treated with just silver or just vancomycin fared much worse. Half of the mice that got silver died, along with 90% of the mice treated with antibiotics. ...
http://www.latimes.com/news/science/la-sci-antibiotics-silver-20130620,0,6215677.story