Copper has a rich history—and a newfound appreciation in modern times. The antimicrobial benefits of copper were first recognized by the Egyptians circa 2600 BC. In Ancient Egypt, the metal was used to sanitize drinking water and treat chest wounds, as well as other infections, scalds, and itching. Recently, the use of copper containers for drinking has been revisited as a low-cost way to fight infections in developing countries. Copper has garnered renewed interest as a biocidal agent. “The spread of antibiotic resistance through selective pressure began and today has made antibiotic-resistant bacteria ubiquitous in hospitals, nursing homes, food processing plants, and animal breeding facilities,” according to the authors of a review published in Applied and Environmental Microbiology. “This has raised the need for different approaches to keep pathogenic microorganisms at bay. One such alternative is the use of copper surfaces in hygiene-sensitive areas.” Here’s a closer look at how copper works to combat infection and potential uses for this wonder metal. Other uses in history Like the Egyptians, the Greeks liked copper, too. This metal was found in copious quantities on the island of Cyprus, from which copper derives its name. In Ancient Greece, copper was used in wound dressings, particularly for leg ulcers. Dry copper was sprinkled into the dressings of fresh wounds to prevent infections. The Romans used copper to treat venereal diseases and non-healing chronic ulcers. Intriguingly, during the two great Cholera epidemics during the 19th century, copper workers evaded the outbreak thanks to the metal’s antimicrobial properties. In the 19th and 20th centuries, inorganic copper preparations were used to treat chronic adenitis, impetigo, eczema, tuberculosis, syphilis, lupus, and more. Its use continued until 1932 when antibiotics were made commercially available. An appreciation for the infection-fighting prowess of copper, however, was lost to time for a couple of reasons. First, scientists didn’t understand how it worked to fight infections. Second, interest in antibiotics supplanted interest in copper. Today, we understand copper better, and there has been a resurgence in its therapeutic uses. Contact killer of bacteria The study of the antimicrobial properties of metallic copper surfaces gained considerable momentum when the Environmental Protection Agency (EPA) registered almost 300 different copper surfaces as antimicrobial in 2008. Clinical research has examined its use in door handles, bathroom fixtures, and bed rails. To date, copper has demonstrated efficacy in annihilating a laundry list of bacterial pathogens, including Legionella, Escherichia coli, Clostridium difficile, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant Enterococcus. Intriguingly, researchers in the 1990s found that Legionella was much less likely to grow on copper pipes compared with plastic or steel ones. Other research has demonstrated that although E. coli O157 can last more than 28 days on stainless-steel surfaces, it survives on copper surfaces for mere minutes. But what is copper’s mechanism of action? “At the current state of knowledge, it appears that contact killing proceeds by successive membrane damage, copper influx into the cells, oxidative damage, cell death, and DNA degradation,” the authors of the aforementioned review in Applied and Environmental Microbiology suggested. “Clearly, this sequence of events is still tentative, and further work on contact killing is required to offer more-detailed molecular insight into the process,” they wrote. Notably, higher copper content of alloys, higher humidity, and higher temperature boosted the efficacy of contact killing by copper. A dose-dependent relationship exists between the efficacy of killing bacteria and copper concentration. On a related note, the addition of anti-corrosion inhibitors or a thick copper oxide layer decreases the efficacy of copper surfaces. “From what is known about the mechanism of contact killing, it appears clear that a clean copper surface, free of oxide, wax, or other coating agents, will always be active in contact killing,” the review authors wrote. Copper vs. COVID-19 The ability of copper to wipe out viruses was first demonstrated back in 1958. In the midst of the current COVID-19 pandemic, researchers have taken great interest in any therapeutic intervention capable of killing the novel coronavirus. Use of copper may fit this bill, according to the results of a review article recently published in Diagnostic Microbiology and Infectious Disease: “A variety of respiratory pathogenic agents such as influenza, SARS-CoV, MERS-CoV, and HCoV [human coronavirus] have been exposed to a variety of copper forms (copper alloy dry surface, sodium copper, ionic copper oxide, copper iodide, Cu2+, and lay copper) in several cultivating media (MDCK, metal, textile, aqueous solution, dry surfaces), having similar results and arriving at the same conclusion: copper is capable to inhibit, inactivate, reduce, and irreversibly destroy coronavirus, influenza virus, and other pathogenic agents in a matter of minutes.” In an article published earlier this year in The New England Journal of Medicine, researchers demonstrated that SARS-CoV-2 was viable on plastic and stainless steel surfaces for up to 3 days, but was eliminated on copper after 4 hours. Other respiratory viruses that succumb to the effects of copper are influenza H1N1 and influenza A. Copper to fight fungi The antifungal activity of copper has been less studied compared with its capabilities against bacteria. Nevertheless, copper has been shown to be effective against Fusarium spp., Penicillium chrysogenum, and Candida albicans, with a mechanism of action similar to that of contact-killing of bacteria. Copper can also prevent the germination of fungal spores in these fungal types. Scientists have demonstrated that copper starts killing fungi through widespread membrane damage, which is followed by the obliteration of vacuoles and the promotion of oxidative stress. Clinical uses A variety of clinical applications have been suggested for copper. For instance, researchers have suggested that copper oxide or nanoparticles can be used to impregnate filters, clothing, and face masks to fight viruses and bacteria. Some of these uses have already shown promise in emerging research. In a clinical trial published in the American Journal of Infection Control, a hospital-based study demonstrated that the utilization of copper fabrics including bed linen, clothing, and towels for a period of 3 months decreased the necessity for antibiotic treatment, duration of antibiotic therapy, daily doses of antibiotics, and the number of days with fever in patients. Importantly, the copper fabrics did not cause skin irritation or other adverse effects. Copper may also be useful as a biocidal surface material, such as doorknob handles. One early adopter of copper surfaces was Pullman Regional Hospital, a level IV trauma center in Washington State that has equipped an 85,000-square-foot facility with copper faucets, basins, IV poles, and access buttons. Source
