Medicine has changed a lot in the last hundred years. We have better technology to look for problems, and if we find one we are much more likely to be able to fix it. And one of the most important fixes is that these days we have antibiotics, which are really good at killing off harmful bacteria, or at least they have been so far. But the more we use those antibiotics, the more bacteria develop resistance to them, so we have to keep finding new ones that the bacteria haven't figured out how to fight yet, which is why scientists are looking at the possibility of bringing metal back into our antibacterial arsenal. 
 

Metals like copper and silver have been used to kill bacteria for thousands of years, even before we knew what bacteria were. One of the oldest books in the world, an Egyptian medical text called the Edwin Smith Papyrus, describes the use of copper for preventing infections in chest wounds. And many ancient cultures believed that copper and silver pots kept water safe to drink for longer. Then, in 1928, a guy named Alexander Fleming came along and found some funky mold growing in his lab and promptly changed history forever. He had discovered penicillin, the first of many antibiotics, and when it was released, the world went crazy for it. Antibiotics were hailed as "miracle drugs" and medical metals were all but forgotten about. 
 
If only it were that easy, though. Bacteria evolve fast, and highly resistant bacteria seem to show up almost as fast as we can invent new drugs. The antibiotics work a bit like an arrow, precisely hitting one weak point in the target. It works great up until the weak point is covered up, when bacteria evolve antibiotic resistance. But if today's antibiotics are more like arrows, metals act like grenades. They hit bacteria harder and in multiple places at once, making it much more difficult for them to evolve resistance. Back in the 1980s, researchers noted that bacteria landing on surfaces made of copper, or alloys that contain copper, like bronze and brass, usually die off within a few minutes or hours. 
 
It's a process known as "contact killing", and recently health professionals have started using it to their advantage. Hospitals across the world are studying what happens when they switch out stainless steel surfaces like door handles and bed rails with copper and brass. One 2010 study in Birmingham, England studied the bacteria-fighting properties of copper and brass. They found 90 to 100 percent fewer bacteria on copper and brass surfaces than on stainless steel, even after six months. And only the steel surfaces had MRSA, a multi-drug resistant bacteria that is often fatal. 
 
Scientists aren't clear on all the details when it comes to copper's contact killing, but it probably has to do with electric charge. Positive copper ions dissolve off the metal surface attracted to the negative charges on the bacterial membrane. Those ions punch more holes in the membranes, letting more copper in. Once loose in the cell, the metal ions can wreak all kinds of havoc. Through various reactions, copper ions can generate high-energy hydroxyl radicals, an oxygen bonded to a hydrogen with an unpaired electron that really wants to bond with stuff. They will react with and damage pretty much any biological molecule, including DNA, proteins, and carbohydrates, which makes it great at killing bacteria. 
 
But even though it's so deadly, small amounts of copper, like many other metals, are important for life. Right now, for instance, copper is working inside proteins that keep your skin elastic, produce the skin pigment melanin, and use oxygen to make energy. Bacteria also need copper, and figuring out how they process it will be a big part of understanding how best to use it against them.
 
Another metal that's turning out to be a useful weapon against bacteria is silver, and, unlike copper, we don't know of any useful functions for silver inside cells. It can be deadly, even in tiny amounts, if it gets in. In case you are now staring at your jewelry in horror, I should mention that silver metal in that bulky form is harmless. It's just too unreactive. On the other hand, particles of nano-silver, just a few billionths of a meter across, might be an important part of the future of medicine. 
 
Things behave very differently at that scale. Their tiny size gives nanoparticles a lot more surface area, making them much more reactive. Nano-silver is already being embedded into or used as a surface coating for medical implants, releasing metal ions slowly and steadily over time to kill bacteria. It's also being studied as an antibacterial agent in fields like dentistry, eye treatments, surgery, and pharmaceuticals. 
 

But don't expect to be popping copper or nano-silver pills to cure infections just yet. Ingesting something isn't the same as using it as a surface, and researchers are still studying how these metals interact with bacteria and plain old cells in the human body. But it does look like those ancient Egyptians were on to something. 
 

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