Researchers from Boston University have found how silver can enhance the effectiveness of existing antibiotics and fight infections against bacteria which have developed resistance to a broad range of antibiotics. The study, published in the latest issue of Science Translational Medicine, can become the forerunner of great improvements in treatments against difficult to treat bacterial infections.
Ancient civilizations, like the Greek, Phoenician and Egyptian, used metals, such as gold and copper, to build tools, weapons and their armor. The third most used metal, silver, was surprisingly used for another purpose, too. They had discovered that food and water were best preserved in silver containers. Hippocrates, the father of medicine, used silver to treat ulcer and skin wounds. Several other medical uses of silver are documented through history, long before the discovery of microbes and until the discovery of antibiotics [pdf].
Those who haven’t fallen asleep during Biology 101 class should probably know that antibiotics are substances produced naturally by some microorganisms in nature. They make antibiotics to protect themselves from bacteria, which can infect them and kill them. Just like harmful bacteria infect and make humans sick. Since Alexander Fleming discovered (accidentally) penicillin, the first ever antibiotic, numerous antibiotics have been found and isolated from other microorganisms. But the extensive, inappropriate use of antibiotics has helped bacteria to acquire resistance and survive over the years.
This has led scientists to find new and better antibiotics or to find ways to make existing antibiotics more effective. Distinguished Professor James Collins is focusing on the latter. In this study, his colleagues in the Collins lab have found how silver exerts its bactericidal activity. They used Escherichia coli, a commonly used bacterium in research labs, and noticed that when silver was added to the culture, the bacterial proteins did not fold correctly (therefore were not fully functional) and the metabolism was severely damaged leading to overproduction of waste, and often toxic, molecules. All these affected the outer layer of bacteria, the membrane which protects the bacterium, making it more permeable.
The latter made the researchers think that silver could help more antibiotics pass through this protective barrier and kill the bacterium. Indeed, when they added tetracycline, a commonly used antibiotic, together with silver to the culture of a tetracycline-resistant bacterium, the bacterium was killed.
All these look great, especially when the research team found that it is not toxic to mice or to human cells in culture. Collins and his team demonstrated further the synergistic effect of silver with antibiotics in mouse models, where antibiotics alone did not fight bacterial infections but in combinations, the results were even 100 times more efficient.
It seems that silver throws a punch in the stomach of bacteria. But “we’ll have to address the toxicity very carefully” says Vance Fowler, an infectious-disease physician at Duke University in Durham, North Carolina. However, the results are very encouraging Collins says, scientists working on antibiotics resistance can now further study “what features of silver caused the helpful effects, so they can look for non-toxic versions.” And definitely, this should never mean that we can continue with the unnecessary and excessive use of antibiotics.