Peer-reviewed research papers discussing the antimicrobial properties of copper-based metals
Here is a library of published papers and conference posters covering the laboratory and clinical studies conducted on the antimicrobial characteristics of solid copper and copper alloys over the last 20 years. Some papers are accessible here as pdfs, others have links to entries in various scientific libraries where full papers can be accessed via a subscription or for a cost.
If you have a paper to suggest we include here, please contact Marleine Williams, Project Co-ordinator, Copper Development Association.
Browse the entire list or use the category filters below.
Seema Rai, Bruce E Hirsch, Hubert H Attaway, Richard Nadan, S Fairey, J Hardy, G Miller, Donna Armellino, Wilton R Moran, Peter Sharpe, Adam Estelle, J H Michel, Harold T Michels and Michael G Schmidt
Study investigating the impact of copper surfaces on the bacterial burden found on high-touch surfaces of phlebotomy chairs in an outpatient infectious disease clinic. Quantitative cultures were obtained from phlebotomy chairs located in an outpatient infectious diseases practice. Results from control (wood/composite) chairs and the copperized therapy chairs were compared. A total of 437 patients used the chairs during the 15-week study period.
Libin Zhu, Jutta Elguindi, Christopher Rensing, Sadhana Ravishankar, Article in Food Microbiology 30 (2012) 303-310. Copyright 2011 Elsevier Ltd
Copper has shown antibacterial effects against foodborne pathogens. The objective of this study was to evaluate the antibacterial activity of copper surfaces on copper resistant and sensitive strains of Salmonella enterica. Six different copper alloy coupons (60-99.9% copper) were tested along with stainless steel as the control. The coupons were surface inoculated with either S. Enteritidis or one of the 3 copper resistant strains, S. Typhimurium S9, S19 and S20; stored under various incubation conditions at room temperature; and sampled at various times up to 2 h. The results showed that under dry incubation conditions, Salmonella only survived 10-15 min on high copper content alloys. Salmonella on low copper content alloys showed 3-4 log reductions. Under moist incubation conditions, no survivors were detected after 30 min-2 h on high copper content alloys, while the cell counts decreased 2-4 logs on low copper content coupons. Although the copper resistant strains survived better than S. Enteritidis, they were either completely inactivated or survival was decreased. Copper coupons showed better antimicrobial efficacy in the absence of organic compounds. These results clearly show the antibacterial effects of copper and its potential as an alternative to stainless steel for selected food contact surfaces.
S L Warnes, V Caves and C W Keevil, Environmental Healthcare Unit, University of Southampton, Highfield, Southampton SO17 1BJ, UK.Journal Article: Environmental Microbiology (impact factor: 5.5). 12/2011; DOI:10.1111/j.1462-2920.2011.02677.x PubMed
Peter A Sharpe, MBA, EDAC, and Michael G Schmidt, MA, PhD. Control and mitigation of healthcare-acquired infections: Designing clinical trials to evaluate new materials and technologies. Health Environments Research & Design Journal, 5(1), 94-115. 2011.
Hospitals clean environmental surfaces to lower microbial contamination and reduce the likelihood of transmitting infections. Despite current cleaning and hand hygiene protocols, hospitalacquired infections (HAIs) continue to result in a significant loss of life and cost the U.S. healthcare system an estimated $45 billion annually. Stainless steel and chrome are often selected for hospital touch surfaces for their "clean appearance," comparatively smooth finish, resistance to standard cleaners, and relative effectiveness for removing visible dirt during normal cleaning. Designers use wood surfaces for aesthetics; plastic surfaces have become increasingly endemic for their relative lower initial cost; and "antimicrobial agents" are being incorporated into a variety of surface finishes. This paper concentrates on environmental surface materials with a history of bactericidal control of infectious agents and focuses on the methods necessary to validate their effectiveness in healthcare situations. Research shows copper-based metals to have innate abilities to kill bacteria in laboratory settings, but their effectiveness in patient care environments has not been adequately investigated. This article presents a research methodology to expand the evidence base from the laboratory to the built environment. For such research to have a meaningful impact on the design/specifying community, it should assess typical levels of environmental pathogens (i.e., surface "cleanliness") as measured by microbial burden (MB); evaluate the extent to which an intervention with copper-based materials in a randomized clinical trial affects the level of contamination; and correlate how the levels of MB affect the incidence of infections acquired during hospital stays.
Karpanen T J, Casey A L, Lambert P A, Cookson B D, Nightingale P, Miruszenko L and Elliott T S J. Infection Control and Hospital Epidemiology
Objective: To determine whether copper incorporated into hospital ward furnishings and equipment can reduce their surface microbial load.
Design: A crossover study.
Setting: Acute care medical ward with 19 beds at a large university hospital.
Methods: Fourteen types of frequent-touch items made of copper alloy were installed in various locations on an acute care medical ward. These included door handles and push plates, toilet seats and flush handles, grab rails, light switches and pull cord toggles, sockets, overbed tables, dressing trolleys, commodes, taps, and sink fittings. Their surfaces and those of equivalent standard items on the same ward were sampled once weekly for 24 weeks. The copper and standard items were switched over after 12 weeks of sampling to reduce bias in usage patterns. The total aerobic microbial counts and the presence of indicator microorganisms were determined.
Results: Eight of the 14 copper item types had microbial counts on their surfaces that were significantly lower than counts on standard materials. The other 6 copper item types had reduced microbial numbers on their surfaces, compared with microbial counts on standard items, but the reduction did not reach statistical significance. Indicator microorganisms were recovered from both types of surfaces; however, significantly fewer copper surfaces were contaminated with vancomycin-resistant enterococci, methicillin-susceptible Staphylococcus aureus, and coliforms, compared with standard surfaces.
Conclusions: Copper alloys (greater than or equal to 58% copper), when incorporated into various hospital furnishings and fittings, reduce the surface microorganisms. The use of copper in combination with optimal infection-prevention strategies may therefore further reduce the risk that patients will acquire infection in healthcare environments.
S L Warnes and C W Keevil, Applied and Environmental Microbiology, September 2011.
Contaminated touch surfaces have been implicated in the spread of hospital-acquired infections, and the use of biocidal surfaces could help to reduce this cross-contamination. In a previous study we reported the death of aqueous inocula of pathogenic Enterococcus faecalis or Enterococcus faecium isolates, simulating fomite surface contamination, in 1 h on copper alloys, compared to survival for months on stainless steel. In our current study we observed an even faster kill of over a 6-log reduction of viable enterococci in less than 10 min on copper alloys with a "dry" inoculum equivalent to touch contamination. We investigated the effect of copper(I) and copper(II) chelation and the quenching of reactive oxygen species on cell viability assessed by culture and their effects on genomic DNA, membrane potential, and respiration in situ on metal surfaces. We propose that copper surface toxicity for enterococci involves the direct or indirect action of released copper ionic species and the generation of superoxide, resulting in arrested respiration and DNA breakdown as the first stages of cell death. The generation of hydroxyl radicals by the Fenton reaction does not appear to be the dominant instrument of DNA damage. The bacterial membrane potential is unaffected in the early stages of wet and dry surface contact, suggesting that the membrane is not compromised until after cell death. These results also highlight the importance of correct surface cleaning protocols to perpetuate copper ion release and prevent the chelation of ions by contaminants, which could reduce the efficacy of the surface.
Panos A Efstathiou, European Infectious Disease, 2011;5(2):125-8
Recent work investigating the antimicrobial characteristics of copper has led to a re-evaluation of the role of this essential metal in healthcare. While ancient civilisations used copper for its health benefits it seems its usefulness has been forgotten. The requirement for evidence-based interventions for infection control has been the driver behind recent scientific assessments of the benefits of copper. Ten years of laboratory research has led to clinical trials confirming a very significant and continuous reduction in environmental bioburden in a number of healthcare settings globally. The newest and most comprehensive clinical research has now reported an impressive 40% reduction in healthcare-associated infections in intensive care units (ICUs) where copper was incorporated in key touch surfaces. The deployment of copper touch surfaces should be considered as an additional infection control measure to reduce care costs and improve bed availability and patient outcomes.
W R Moran, H H Attaway, M G Schmidt, J F John, C D Salgado, K A Sepkowitz, R J Cantey, L L Steed, H T Michels. Poster presented at the American Hospital Association and Health Forum Leadership Summit 2011, July 17-19, 2011, San Diego, CA.
Each year hospital--‐acquired infections (HAI) result in a substantial loss of life and an additional cost to the US healthcare system of $45 billion dollars. Evidence is presented illustrating how risk mitigation of the environmental burden resulted in a concomitant mitigation of the HAI rates for patients treated in rooms with antimicrobial copper touch surfaces. A discussion of the complexities and costs associated with effectively applying antimicrobial copper touch surfaces within the built environment will facilitate an understanding of the need for a design that makes use of emerging infection control solutions to fight HAIs in a pragmatic and aesthetically satisfying way.
Mark Tur, Proceedings of 2011 European Design 4 Health Conference, Sheffield, UK. 13-15th July 2011
There is now no doubt that copper and copper alloys possess the strongest antimicrobial efficacy of all common materials under normal indoor conditions. This is leading to the adoption of copper alloys for touch surfaces such as door furniture, handrails and trolleys to reduce contamination on frequently touched surfaces and help reduce infection in healthcare environments. Copper's efficacy has been demonstrated both in the laboratory and, more pertinently, at a set of eight geographically diverse clinical trials. The latest results and new experiences from these trials will be reported here.
There is general acceptance that high environmental bioburden will tend to increase infections, but the case has, perhaps surprisingly, to be proven. In 2010, the Department of Health turned the spotlight on the influence of the environment on the incidence of infection. A selected review of the existing evidence will be presented.
In the UK to date, there have been a small number of early adopters of Antimicrobial Copper, and a case study will be presented of one such specialist unit, the brief being 'to set the gold standard for infection control'. This will work through conception, choice, installation and use to maintenance.
In order to support the understanding and deployment of copper alloys, a technology rich website has been developed to act as a global resource. This will be introduced and key areas for designers and architects will be highlighted.
Anton Shufutinsky, Harold Michels, Wilton Moran, Adam Estelle, James Michel, Chris Dreska, Dennis Simon. Poster presented at 2011 US Armed Forces Public Health Conference.
Explains the potential application of Antimicrobial Copper surfaces as a method for preventing surface and airborne microbial contamination in military healthcare facilities, food handling operations, and other occupational settings.
C Espírito Santo, E W Lam, C G Elowsky, D Quaranta, D W Domaille, C J Chang, and G Grass, 2011. Bacterial killing by dry metallic copper surfaces. Appl. Environ. Microbiol. 77: 794-802
Metallic copper surfaces kill microbes on contact, decimating their populations, according to a paper in the February 2011 issue of the journal Applied and Environmental Microbiology. They do so literally in minutes, by causing massive membrane damage after about a minute's exposure, says the study's corresponding author, Gregor Grass of the University of Nebraska, Lincoln. This is the first study to demonstrate this mechanism of bacteriocide.
"When microbes were exposed to copper surfaces, we observed contact killing to take place at the rate of tens to hundreds of millions of bacterial cells within minutes," says Grass. "This means that usually no live microorganisms can be recovered from copper surfaces after exposure."
Thus, such surfaces could provide a critical passive defense against pathogens in hospitals, where hospital-acquired infections are becoming increasingly common and costly, killing 50,000-100,000 Americans annually, and costing more than $8 billion, according to one estimate. Still, Grass cautions that "metallic copper surfaces will never be able to replace other hygiene-improving methods already in effect," although they "will certainly decrease the costs associated with hospital-acquired infections and curb human disease as well as save lives." However, he expects this strategy to be inexpensive, because "the effect does not wear off."
Critically, the researchers provide strong evidence that genotoxicity through mutations and DNA lesions is not a cause of dry copper's antimicrobial properties. This is important, because mutations can cause cancer in animals and humans, and the lack of such mutations in bacteria from copper means that copper does not endanger humans.
The relevant experiment was particularly interesting. The bacterium, Deinococcus radiodurans, is unusually resistant to radiation damage, as its DNA repair mechanisms are especially robust. The hypothesis: if metallic copper kills by causing DNA damage, D. radiodurans should be immune to copper. It is not.
It is important to note that only dry copper surfaces are amazingly lethal to bacteria. The difference between dry and wet surfaces, such as copper pipes, is that only dry surfaces are inhospitable environments for bacterial growth. Bacteria can easily grow and reproduce in wet environments, and in so doing, they can develop resistance to copper. Resistance has not been observed to develop on dry copper surfaces.
Gregor Grass, Christopher Rensing and Marc Solioz, Appl. Environ. Microbiol. March 2011, pp 1541-1547. Vol 77, No 5. doi: 10.1128/AEM.02766-10,
Bacteria, yeast, and viruses are rapidly killed on metallic copper surfaces and the term 'contact-killing' has been coined for this process. While the phenomenon has already been known in ancient times, it is currently receiving renewed attention. This is due to the potential use of copper as an antibacterial material in health care settings. Contact-killing was observed to take place at the rate of seven to eight logs per hour or even minutes and no live microorganisms were generally recovered from copper surfaces after prolonged incubation. The antimicrobial activity of copper and copper alloys is now well established and copper has recently been registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material. In several clinical studies, copper has been evaluated for use on touch-surfaces such as door handles, bathroom fixtures, or bed rails, in attempts to curb nosocomial infections. In connection to these new applications of copper, it becomes of importance to understand the mechanism of contact-killing as it may bear on central issues, such as the possibility of the emergence and spread of resistant organisms, cleaning procedures, and questions of material and object engineering. Recent work has shed light on mechanistic aspects of contact-killing. These findings will be reviewed here and juxtaposed to the toxicity mechanisms of ionic copper. The merit of copper as a hygienic material in hospital and related settings will also be discussed.
Marais F et al, J Hosp Infect (2009), doi:10.1016/j.jhin.2009.07.010.
A comparative controlled study was conducted at a busy walk-in primary healthcare clinic (PHC) in Grabouw, a rural region of the Western Cape, South Africa, to demonstrate antimicrobial efficacy of copper touch surfaces in reducing bioburden in a community healthcare facility.
Kristopher Page, Michael Wilson and Ivan P Parkin, University College London. January 2009. J. Mater. Chem. 2009 DOI: 10.1039/b818698g
Environmental surfaces and their role in the epidemiology of hospital-acquired infections (HAIs) have become an area of great scientific interest, particularly in light of the much publicised cases of infections due to methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile in UK hospitals. This feature article sets out to examine the role of surfaces and the inanimate environment in the spread of HAIs, and looks at various antimicrobial techniques being researched to reduce microbial contamination of surfaces. Preventative measures such as coatings which reduce initial microbial adhesion to surfaces will be considered alongside actively antimicrobial measures which inactivate microorganisms already adherent to a surface. The principal focus of this feature article will be given to light-activated antimicrobial surfaces such as the photocatalyst TiO2 and surfaces with embedded photosensitisers. Surfaces which release antimicrobial compounds or metal ions such as silver and copper are also examined, alongside materials which kill microbes upon contact. The widespread research and development of these antimicrobial surfaces is of great importance in maintaining acceptable levels of hygiene in hospitals and will help to fight the spread of HAIs via the contamination of inanimate surfaces in the healthcare environment.
S W J Gould, M D Fielder, A F Kelly, M Morgan, J Kenny, D P Naughton,Annals of Microbiology, 59 (1) 151-156 (2009)
Hospital-acquired infections (HAI) are a major problem worldwide and controlling the spread of these infections within a hospital is a constant challenge. Recent studies have highlighted the antimicrobial properties of copper and its alloys against a range of different bacteria.
The objective of this study was to evaluate the antimicrobial properties of copper compared to stainless steel against a range of clinically important pathogens. These pathogens consisted of five isolates of each of the following organisms; meticillin resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Escherichia coli, vancomycin-resistant Enterococci (VRE) and Panton-Valentine Leukocidin positive community acquired-MSSA (PVL positive CA-MSSA, MRSA, P. aeruginosa, E.coli and CA-MSSA isolates were not detectable after a median time of 60 minutes. No detectable levels for all VRE iosolates were determined after a median time of 40 minutes. However, for all isolates tested the stainless steel had no effect on the survival of the bacteria and levels remained similar to the time zero count.
The results of this study demonstrate that copper has a strong antimicrobial effect against a range of clinically important pathogens compared to stainless steel and potentially could be employed to aid the control HAI.
A L Casey, P A Lambert, L Miruszenko, T S J Elliott. October 2008
Poster presented at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), October 2008.
C D Salgado, K A Sepkowitz, T Plaskett, J F John, J R Cantey, H H Attaway, L L Steed, H T Michels, M G Schmidt. October 2008.
This study sought to determine the microbial burden (MB) on frequently touched inanimate objects in the ICU rooms of patients at three different US hospitals.The findings showed that Staphylococci were the predominant organism isolated within this MB.
Objects found in ICU rooms can serve as a reservoir for the spread of bacteria, particularly staphylococci, to patients, healthcare workers, and visitors. Objects in close proximity to patients pose the greatest risk, particularly bed rails.
Patient acquisition of organisms that were recovered from ICU rooms may lead to healthcare-acquired infections resulting in substantial morbidity and mortality. Future studies should focus on strategies to reduce high level bacterial contamination of common objects in patient rooms and potential spread of these bacteria in order to potentially reduce healthcare-acquired infections.
H Michels, W Moran and J Michel, International Journal of Metalcasting, Summer 2008, pp 47-56
Discusses the antimicrobial properties of copper alloys and their potential to reduce the amount of certain bacteria on frequently touched surfaces. Efficacy data address other materials and the effects of tarnishing, bacteria concentration and repeated contamination. EPA testing, results and registration are highlighted.
L. J. Wheeldon, T. Worthington, P. A. Lambert, A. C. Hilton, C. J. Lowden and T. S. J. Elliott, Journal of Antimicrobial Chemotherapy 2008 62(3):522-525; doi:10.1093/jac/dkn219.
Methods: Antimicrobial efficacy was assessed using a carrier test method against dormant spores, germinating spores and vegetative cells of C. difficile (NCTC 11204 and ribotype 027) over a 3h period in the presence and absence of organic matter.
Results: Copper metal eliminated all vegetative cells of C. difficile within 30 min, compared with stainless steel which demonstrated no antimicrobial activity (P < 0.05). Copper significantly reduced the viability of spores of C. difficile exposed to the germinant (sodium taurocholate) in aerobic conditions within 60 min (P < 0.05) while achieving a 2.5 log reduction (99.8% reduction) at 3 h. Organic material did not reduce the antimicrobial efficacy of the copper surface (P > 0.05).
Conclusions: The use of copper surfaces within the clinical environment and application of a germination solution in infection control procedures may offer a novel way forward in eliminating C. difficile from contaminated surfaces and reducing CDAD.
H T Michels and D G Anderson, pp 185-190, Metal Ions in Biology and Medicine: Vol 10, Eds Ph Collery, I Maymard, T Theophanides, L Khassanova, T Collery. John Libbey Eurotext, Paris © 2008
Discusses potential impact of antimicrobial copper alloys on amount of certain bacteria on frequently touched surfaces in healthcare settings. Describes the steps required to make public health claims and summarises EPA test protocols and results.
L Weaver, H T Michels, and C W Keevil, Journal of Hospital Infection, Vol 68, Issue 2, pp 145-151, February 2008
Compares the viability of Clostridium difficile on copper and stainless steel. Reports a significant reduction of Clostridium difficile was observed on alloys with >70% copper content while no reduction is observed on steel. Suggests use of copper alloys in hospitals may reduce the levels of Clostridium difficile on frequently touched surfaces.
S Mehtar, I Wiid, and S D TodorovJournal of Hospital Infection, Vol. 68, Issue 1, pp 45-51, January 2008
Compares the viability of MRSA, Klebsiella pneumonia, Pseudomonas aeruginosa, Acinetobacter baumannii, Candida albicans and Mycobacterium tuberculosis on copper alloys, stainless steel and PVC. Results illustrate copper's ability to kill pathogens most commonly associated with hospital-acquired infections. No effect was observed on PVC and stainless steel.
J O Noyce, H Michels and C W Keevil, Applied and Environmental Microbiology, pp 2748 - 2750, Vol 73, No 8, April 2007
Uses fluorescent microscopy to compare viability of Influenza A on copper and stainless steel. Copper showed a 4-log reduction after 6 hours while steel only showed a 1-log reduction after 24 hours.
H T Michels, D G Anderson, J O Noyce, S A Wilks and C W Keevil, Proceedings of the Sixth International Copper-Cobre Conference, pp 121-133, Vol I, August 2007
Describes potential healthcare applications and barriers for antimicrobial copper alloys. Authors review efficacy data against various organisms and EPA testing.
S A Wilks, H T Michels and C W Keevil, International Journal of Food Microbiology, 111, September (2006), pp 93-98.
Compares the viability of Listeria monocytogenes on various copper alloys and stainless steel. Copper-based alloys produced a significant reduction in viability compared to stainless steel. Suggests materials selection could impact bioload in various environments.
Copper and copper alloys are engineering materials that are durable, colourful and recyclable and are widely available in various product forms suitable for a range of manufacturing purposes. Copper and its alloys offer a suite of materials for designers of functional, sustainable and cost-effective products.
Copper and certain copper alloys have intrinsic antimicrobial properties (so-called ‘Antimicrobial Copper’) and products made from these materials have an additional, secondary benefit of contributing to hygienic design. Products made from Antimicrobial Copper are a supplement to, not a substitute for standard infection control practices. It is essential that current hygiene practices are continued, including those related to the cleaning and disinfection of environmental surfaces.