Opinion: The crucible
Copper doorknobs could be the latest - and oldest - way to beat the bugs, says Philip Ball
In what sounds like a rather literal interpretation of the old Yorkshire proverb that where there's muck there's brass, a hospital in Birmingham, UK, is hoping to stamp out its superbugs by replacing all its metal fittings with copper ones. The aim is to exploit the discovery, made at the University of Southampton three years ago, that methicillin-resistant Staphylococcus aureus (MRSA) die within an hour or so on copper surfaces, whereas the bacteria survive for days on stainless steel. Indeed, brass - copper alloyed with zinc - performs even better than copper.
Door handles no doubt play a significant part in transmitting MRSA, which afflicts thousands, sometimes fatally, in UK hospitals every year. The Birmingham hospital has been selected because of its expertise in microbiology - but it happens also to have a particularly bad record for MRSA, and the 18-month trial will see if copper can do anything to improve it. Not only door handles but taps, toilet flushes and handrails are going to be replaced with the red metal.
This behaviour of copper is in some ways no great surprise. Heavy metals are of course notoriously toxic, and the antimicrobial properties of silver have become a particular focus of interest because silver ions, while lethal to bacteria, are essentially harmless to humans. Silver oxide has a long history of antimicrobial use, and bacteria-killing silver nanoparticles and nanostructured surfaces are emerging as some of the first commercial products of nanotechnology. SilvaSorb gel, sold by the US company AcryMed and consisting of a silver compound bound in a hydrogel for controlled release, is already marketed as an agent against MRSA.
Copper, meanwhile, has a history of medical use that goes back almost beyond recorded history. The Egyptians used verdigris - copper acetate, made by reacting copper metal with vinegar fumes - for treating eye infections. A manuscript called the Smith papyrus, dating from 2600-2200 BC, records the use of copper salts as sterilizers for drinking water and for dressing wounds. The Greeks, who got their copper from Cyprus - whence the Latin cuprum - recommended the oxide mixed with honey as an antiseptic. Copper also has antifungal properties: the sulfate is the active ingredient in Bordeaux mixture, used to protect grape vines.
But as Paracelsus was wont to remark, the poison is in the dose, and if a little copper does you good (we need about 1 mg of it every day), too much turns the stomach. At least, you had better hope so, for an overdose of copper can kill if it is not vomited out. Yet even this has its uses: 'purgatives' were a favourite aspect of ancient medicine, and Pliny says that copper oxide is excellent for clearing the stomach (it will also kill intestinal worms, he adds). Paracelsus himself was fond of copper sulfate (vitriol of Venus, in the alchemical terminology) as a medicine, saying 'in vitriol so great and powerful a tincture lurks as an inexperienced person could scarcely believe'.
There are, happily, more sophisticated ways of exploiting the biological behaviour of copper. Its salts may act as anti-inflammatory agents - in particular, the copper salts of aspirin and ibuprofen are more active than those drugs on their own. This makes copper effective for treating arthritis and other rheumatic conditions. The story has it that in 1939 the German physician Werner Hangarter noticed that copper miners in Finland suffered less from arthritis than did the population as a whole. Hangarter later researched the use of organic copper complexes to combat rheumatoid arthritis; but although copper aspirinate showed promise, it never became a common treatment.
Here of course is the seed of the belief that a copper bracelet or anklet is good for the joints. But even if we shouldn't scoff at the notion out of hand, nonetheless it displays the typically infuriating tendency of alternative medicines to turn pharmacology into something talismanic: it seems akin to curing a headache by sticking aspirin pills (or better still, willow bark) to your wristwatch.
Making brass doorknobs the frontline defence against MRSA is therefore part of an old tradition. The fact that brass works better than copper could possibly have something to do with the chemistry of zinc, but I can't help suspecting that, as with the nobility of gold, the reason might stem from the surface electronic structure in the alloy. That would make copper antimicrobial activity a subtle quantum effect, uniting the very new and the very ancient.
Philip Ball is a science writer based in London