Copper and its alloys (brasses, bronzes, cupronickel, copper-nickel-zinc, and others) are natural antimicrobial materials. Ancient civilizations exploited the antimicrobial properties of copper long before the concept of microbes became understood in the nineteenth century.Dollwet, H. H. A. and Sorenson, J. R. J. "Historic uses of copper compounds in medicine", Trace Elements in Medicine, Vol. 2, No. 2, 1985, pp. 80–87."A Brief History of The Health Support Uses of Copper" In addition to several copper medicinal preparations, it was also observed centuries ago that water contained in copper vessels or transported in copper conveyance systems was of better quality (i.e., no or little visible slime or biofouling formation) than water contained or transported in other materials.
The antimicrobial properties of copper are still under active investigation. Molecular mechanisms responsible for the antibacterial action of copper have been a subject of intensive research. Scientists are also actively demonstrating the intrinsic efficacy of copper alloy "touch surfaces" to destroy a wide range of microorganisms that threaten public health.Zaleski, Andrew, As hospitals look to prevent infections, a chorus of researchers make a case for copper surfaces, STAT, September 24, 2020
Mechanisms of action In 1852 Victor Burq discovered that those working with copper had far fewer deaths to cholera than anyone else, and did extensive research confirming this. In 1867 he presented his findings to the French Academies of Science and Medicine, informing them that putting copper on the skin was effective at preventing someone from getting cholera.
The oligodynamic effect was discovered in 1893 as a toxic effect of metal ions on living cells, algae, molds, spores, fungi, viruses, prokaryotic, and eukaryotic microorganisms, even in relatively low concentrations. This antimicrobial effect is shown by ions of copper as well as mercury, silver, iron, lead, zinc, bismuth, gold, and aluminium.
In 1973, researchers at Battelle Columbus LaboratoriesDick, R. J.; Wray, J. A.; Johnston, H. N. (1973), "A Literature and Technology Search on the Bacteriostatic and Sanitizing Properties of Copper and Copper Alloy Surfaces", Phase 1 Final Report, INCRA Project No. 212, June 29, 1973, contracted to Battelle Columbus Laboratories, Columbus, Ohio conducted a comprehensive literature, technology, and patent search that traced the history of understanding the "bacteriostatic and sanitizing properties of copper and copper alloy surfaces", which demonstrated that copper, in very small quantities, has the power to control a wide range of molds, fungi, algae, and harmful microbes. Of the 312 citations mentioned in the review across the time period 1892–1973, the observations below are noteworthy: Copper inhibits Actinomucor elegans, Aspergillus niger, Bacterium linens, Bacillus megaterium, Bacillus subtilis, Brevibacterium erythrogenes, Candida utilis, Penicillium chrysogenum, Rhizopus niveus, Saccharomyces mandshuricus, and Saccharomyces cerevisiae in concentrations above 10 g/L.Chang, S. M. and Tien, M. (1969), Effects of Heavy Metal Ions on the Growth of Microorganisms, Bulletin of the Institute of Chemistry, Academia Sinica, Vol. 16, pp. 29–39. Candida utilis (formerly, Torulopsis utilis) is completely inhibited at 0.04 g/L copper concentrations. Tubercle bacillus is inhibited by copper as simple cations or complex anions in concentrations from 0.02 to 0.2 g/L.Feldt, A. (no year), Tubercle Bacillus and Copper, Munchener medizinische Wochenschrift, Vol. 61, pp. 1455–1456 Achromobacter fischeri and Photobacterium phosphoreum growth is inhibited by metallic copper. Paramecium caudatum cell division is reduced by copper plates placed on Petri dish covers containing infusoria and nutrient media.Oĭvin, V. and Zolotukhina, T. (1939), Action Exerted From a Distance by Metals on Infusoria, Bulletin of Experimental Biology and Medicine USSR, Vol. 4, pp. 39–40. Poliovirus is inactivated within ten minutes of exposure to copper with ascorbic acid.
A subsequent paper probed some of copper's antimicrobial mechanisms and cited no fewer than 120 investigations into the efficacy of copper's action on microbes. The authors noted that the antimicrobial mechanisms are very complex and take place in many ways, both inside cells and in the interstitial spaces between cells.
Examples of some of the molecular mechanisms noted by various researchers include the following: The 3-dimensional structure of proteins can be altered by copper, so that the proteins can no longer perform their normal functions. The result is inactivation of bacteria or viruses. Copper complexes form radicals that inactivate viruses. Copper may disrupt enzyme structures, and functions by binding to sulfur- or carboxylate-containing groups and amino groups of proteins. Copper may interfere with other essential elements, such as zinc and iron. Copper facilitates deleterious activity in superoxide radicals. Repeated redox reactions on site-specific macromolecules generate HO• radicals, thereby causing "multiple hit damage" at target sites. Copper can interact with lipids, causing their peroxidation and opening holes in the cell membranes, thereby compromising the integrity of cells. This can cause leakage of essential solutes, which in turn, can have a desiccating effect. Copper damages the respiratory chain in Escherichia coli cells. and is associated with impaired cellular metabolism. Faster corrosion correlates with faster inactivation of microorganisms. This may be due to increased availability of cupric ion, Cu2+, which is believed to be responsible for the antimicrobial action.Michels, H. T.; Wilks, S. A.; Noyce, J. O.; Keevil, C. W. (2005), Copper Alloys for Human Infectious Disease Control , Presented at Materials Science and Technology Conference, September 25–28, 2005, Pittsburgh, PA; Copper for the 21st Century Symposium In inactivation experiments on the flu strain, H1N1, which is nearly identical to the H5N1 avian strain and the 2009 H1N1 (swine flu) strain, researchers hypothesized that copper's antimicrobial action probably attacks the overall structure of the virus and therefore has a broad-spectrum effect. Microbes require copper-containing enzymes to drive certain vital chemical reactions. Excess copper, however, can affect proteins and enzymes in microbes, thereby inhibiting their activities. Researchers believe that excess copper has the potential to disrupt cell function both inside cells and in the interstitial spaces between cells, probably acting on the outer envelope of cells.BioHealth Partnership Publication (2007): Lowering Infection Rates in Hospitals and Healthcare Facilities - The Role of Copper Alloys in Battling Infectious Organisms, Edition 1, March.
Currently, researchers believe that the most important antimicrobial mechanisms for copper are as follows: Elevated copper levels inside a cell causes oxidative stress and the generation of hydrogen peroxide. Under these conditions, copper participates in the so-called Fenton-type reaction — a chemical reaction causing oxidative damage to cells. Excess copper causes a decline in the membrane integrity of microbes, leading to leakage of specific essential cell nutrients, such as potassium and glutamate. This leads to desiccation and subsequent cell death. While copper is needed for many protein functions, in an excess situation (as on a copper alloy surface), copper binds to proteins that do not require copper for their function. This "inappropriate" binding leads to loss-of-function of the protein, and/or breakdown of the protein into nonfunctional portions.
These potential mechanisms and others are the subject of continuing study by academic research laboratories worldwide.
Antimicrobial efficacy of copper alloy touch surfaces
Copper alloy surfaces have intrinsic properties that destroy many microorganisms. In the interest of protecting public health, especially in healthcare environments with their susceptible patient populations, an abundance of peer-reviewed antimicrobial efficacy studies have been conducted in the past ten years regarding copper's efficacy to destroy E. coli O157:H7, methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus, Clostridioides difficile, influenza A virus, adenovirus, and fungi. Stainless steel was also investigated because it is an important surface material in today's healthcare environments. The studies cited here, plus others directed by the United States Environmental Protection Agency, resulted in the 2008 registration of 274 different copper alloys as certified antimicrobial materials that have public health benefits.
E. coli
E. coli O157:H7 is a potent, highly infectious, ACDP (Advisory Committee on Dangerous Pathogens, UK) Hazard Group 3 foodborne and waterborne pathogen. The bacterium produces potent toxins that cause diarrhea, severe aches, and nausea in infected persons. Symptoms of severe infections include hemolytic colitis (bloody diarrhea), hemolytic uremic syndrome (kidney disease), and death. E. coli O157:H7 has become a serious public health threat because of its increased incidence and because children up to 14 years of age, the elderly, and immunocompromised individuals are at risk of incurring the most severe symptoms.
Efficacy on copper surfaces Recent studies have shown that copper alloy surfaces kill E. coli O157:H7. More than 99.9% of E. coli microbes are killed after just 1–2 hours on copper. On stainless steel surfaces, the microbes can survive for weeks.
Results of E. coli O157:H7 destruction on an alloy containing 99.9% copper (C11000) demonstrate that this pathogen is rapidly and almost completely killed (more than 99.9% kill rate) within ninety minutes at room temperature (20 °C). At chill temperatures (4 °C), more than 99.9% of E. coli O157:H7 are killed within 270 minutes. E. coli O157:H7 destruction on several copper alloys containing 99%–100% copper (including C10200, C11000, C18080, and C19700) at room temperature begins within minutes. At chilled temperatures, the inactivation process takes about an hour longer. No significant reduction in the amount of viable E. coli O157:H7 occurs on stainless steel after 270 minutes.