Scientific References

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.


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Contact Killing of Bacteria on Copper is Suppressed if Bacterial-Metal Contact is Prevented and Induced on Iron by Copper Ions
Salima Mathews, Michael Hans, Frank Mücklich, Marc Solioz, Applied and Environmental Microbiology, April 2013, Vol 79, No 8. Copyright © American Society for Microbiology. doi:10.1128/AEM.03608-12.

Bacteria are rapidly killed on copper surfaces, and copper ions released from the surface have been proposed to play a major role in the killing process.  However, it has remained unclear whether contact of the bacteria with the copper surface is also an important factor.  Using laser interference lithography, we engineered copper surfaces which were covered with a grid of an inert polymer which prevented contact of the bacteria with the surface.  Using Enterococcus hirae as a model organism, we showed that the release of ionic copper from these modified surfaces was not significantly reduced.  In contrast, killing of bacteria was strongly attenuated.  When E.hirae cells were exposed to a solid iron surface, the loss of cell viability was the same as on glass.  However, exposing cells to iron in the presence of 4mM CuSO4 led to complete killing in 100 min.  These experiments suggest that contact killing proceeds by a mechanism whereby the metal-bacterial contact damages the cell envelope, which, in turn, makes the cells susceptible to further damage by copper ions.

Antimicrobial activity of copper surfaces against carbapenemase-producing contemporary Gram-negative clinical isolates
Souli M, Galani I, Plachouras D, Panagea T, Armaganidis A, Petrikkos G, Giamarellou H.

The antimicrobial activity of copper surfaces against a variety of contemporary carbapenemase-producing Gram-negative bacteria representative of the most problematic nosocomial pathogens worldwide was evaluated.

It was concluded that copper has significant antimicrobial activity against multidrug-resistant nosocomial Gram-negative pathogens. This supports the hypothesis that replacement of high-contact materials with copper could reduce the high burden of environmental contamination around high-risk patients. However, this strategy should be seen as an adjunctive measure to established cleaning protocols and to good hygiene practices for prevention of hospital-acquired infections.

4th Department of Internal Medicine, Athens University School of Medicine, University General Hospital 'Attikon', 1 Rimini Str. 124 62, Chaidari, Athens, Greece. J Antimicrob Chemother. 2012 Dec 9. [Epub ahead of print].

Experimental Tests of Copper Components in Ventilation Systems for Microbial Control
Charles Feigley, Jamil Khan, Deborah Salzberg, James Hussey, Hubert Attaway, Lisa Steed, Michael Schmidt and Harold Michels, (2013), HVAC&R Research, 19:1, 53-62

Colonization of HVAC systems by microbes may lead to release of hazardous bioaerosols containing allergens, irritants, odorants or infectious agents to outdoor air, possibly adversely affecting system performance.  Unlike the many common materials used in HVAC systems, copper and copper alloys have ben shown in laboratory investigations to kill bacteria and fungi on contact after several hours.  This study tested copper's antimicrobial properties in comparison with aluminium in full-scale, carefully controlled air-conditioning systems, four with copper heat exchanger facilities and four with aluminium assemblies, at identical airflow rates, temperatures, humidity, and input microbe levels.  Fungal and bacterial loads on copper surfaces in heat exchangers were lower than on aluminium surfaces by factors of 3500 and more than 500, respectively, over a 4-month period.  No statistically significant difference in the release of airborne microbes was detected between copper and aluminium heat exchangers.  The moderate conditions employed in this study, while still within the range commonly found in HVAC systems, possibly prevented the high microbial loading on aluminium heat exchanger surfaces from translating into significant differences in airborne concentrations betweeen copper and aluminium systems.

Horizontal Transfer of Antibiotic Resistance Genes on Abiotic Touch Surfaces: Implications for Public Health
Sarah L. Warnes, Callum J Highmore, and C William Keevil, Centre for Biological Sciences, University of Southampton, Highfield Campus, Southampton, UK. doi: 10.1128/​mBio.00489-12 27 November 2012 mBio vol. 3 no. 6 e00489-12

Horizontal gene transfer (HGT) is largely responsible for increasing the incidence of antibiotic-resistant infections worldwide. While studies have focused on HGT in vivo, this work investigates whether the ability of pathogens to persist in the environment, particularly on touch surfaces, may also play an important role.

Antimicrobial Effect of Copper on Multidrug-resistant Bacteria
G. Steindl, S. Heuberger and B. Springer. Wiener Tierärztliche Monatsschrift – Veterinary Medicine Austria 99 (2012).

Copper has been used for centuries as a therapeutic agent in various cultures around the globe. With the emergence and spread of antibiotic resistance, the use of metallic copper alloys to control pathogenic microorganisms is attracting increasing attention. We investigated the antimicrobial effect of copper on three multidrug-resistant bacterial strains: methicillin-resistant  Staphylococcus aureus sequence type 398, CTX-M-15 producing  Escherichia coli and NDM-1 producing Klebsiella pneumoniae.

Copper coupons were inoculated with bacterial cell suspensions and incubated at room temperature. At set time points, bacteria were resuspended and plated onto nutrient agar and colony-forming units were counted. Results show a more than fivefold log-reduction of viable bacteria for CTX-M-15 producing  E. coli and NDM-1 producing  K. pneumoniae after 60 min of incubation on metallic copper compared to stainless steel. The same reduction of viable bacteria could be demonstrated for methicillin-resistant S. aureus sequence type 398 after 120 min of incubation.

Our data complement scientific evidence for copper´s antimicrobial properties on multidrug-resistant bacteria and suggest that the use of copper surfaces constitutes an approach to support the control of these organisms.

Application of copper to prevent and control infection. Where are we now?
O’Gorman J, Humphreys H, Journal of Hospital Infection (2012),

Background: The antimicrobial effect of copper has long been recognized and has a potential application in the healthcare setting as a mechanism to reduce environmental contamination and thus prevent healthcare-associated infection (HCAI).

Aim: To review the rationale for copper use, the mechanism of its antimicrobial effect, and the evidence for its efficacy.

Methods: A PubMed search of the published literature was performed.

Findings: Extensive laboratory investigations have been carried out to investigate the biocidal activity of copper incorporated into contact surfaces and when impregnated into textiles and liquids. A limited number of clinical trials have been performed, which, although promising, leave significant questions unanswered. In particular there is a lack of consensus on minimum percentage copper alloys required for effectiveness, the impact of organic soiling on the biocidal effect of copper, and the best approach to routine cleaning of such surfaces. Limited information is available on the ability of copper surfaces to eradicate spores of Clostridium difficile.

Conclusion: Additional studies to demonstrate that installing copper surfaces reduces the incidence of HCAI are required and the cost-effectiveness of such intervention needs to be assessed. Further research in a number of key areas is required before the potential benefits of using copper routinely in the clinical setting to prevent and control infection can be confirmed and recommended.

Sustained Reduction of Microbial Burden on Common Hospital Surfaces through Introduction of Copper
Michael G Schmidt, Hubert H Attaway, Peter A Sharpe, Joseph John Jr, Kent A Sepkowitz, Andrew Morgan, Sarah E Fairey, Susan Singh, Lisa L Steed, J Robert Cantey, Katherine D Freeman, Harold T Michels, Cassandra D Salgado J Clin Microbiol July 2012 vol 50

The contribution of environmental surface contamination with pathogenic organisms to the development of healthcare-associated infections (HAI) has not been well defined.  The microbial burden (MB) associated with commonly touched surfaces in intensive care units (ICUs) was determined by sampling six objects in 16 rooms in ICUs in three hospitals over 43 months.

At month 23, copper-alloy surfaces, with inherent antimicrobial properties, were installed onto six monitored objects in 8 of 16 rooms, and the effect that this application had on the intrinsic MB present on the six objects was assessed.Census continued in rooms with and without copper for an additional 21 months.

In concert with routine infection control practices, the average MB found for the six objects assessed in the clinical environment during the preintervention phase was 28 times higher (6,985 CFU/100 cm2; n = 3,977 objects sampled) than levels proposed as benign immediately after terminal cleaning (<250 CFU/100 cm2).

During the intervention phase, the MB was found to be significantly lower for both the control and copper-surfaced objects. Copper was found to cause a significant (83%) reduction in the average MB found on the objects (465 CFU/100 cm2; n = 2714 objects) compared to the controls (2,674 CFU/100 cm2; n = 2,831 objects [P < 0.0001]).

The introduction of copper surfaces to objects formerly covered with plastic, wood, stainless steel, and other materials found in the patient care environment significantly reduced the overall MB on a continuous basis, thereby providing a potentially safer environment for hospital patients, health care workers (HCWs), and visitors.

Supplemental Materials and Methods:

Table S1 - Assessment of the intrinsic microbial burden found on commonly encountered objects before an intervention with antimicrobial copper

Table S2 - Determination of the intrinsic microbial burden associated with six high-touch objects with or without copper surfaces within three ICUs

Figure S1 - Distribution of the microbial burden in the built environment is subject to stochastic forces

Figure S2 - Copper surfaces attenuate the inherent variability of the MB recovered from high-touch objects in the ICU

J Clin Microbiol July 2012 vol. 50 no. 7 2217-2223. Published ahead of print 2 May 2012, doi: 10.1128/JCM.01032-12.

Characterization and Control of the Microbial Community Affiliated with Copper or Aluminum Heat Exchangers of HVAC Systems
Michael G Schmidt, Hubert H Attaway, Silva Terzieva, Anna Marshall, Lisa L Steed, Deborah Salzberg, Hameed A Hamoodi, Jamil A Khan, Charles E Feigley, Harold T Michels. Curr Microbiol, 2012 May 9.

Microbial growth in heating ventilation and airconditioning (HVAC) systems with the subsequent contamination of indoor air is of increasing concern. Microbes and the subsequent biofilms grow easily within heat exchangers. A comparative study where heat exchangers fabricated from antimicrobial copper were evaluated for their ability to limit microbial growth was conducted using a full-scale HVAC system under conditions of normal flow rates using single-pass outside air. Resident bacterial and fungal populations were quantitatively assessed by removing triplicate sets of coupons from each exchanger commencing the fourth week after their installation for the next 30 weeks.

The intrinsic biofilm associated with each coupon was extracted and characterized using selective and differential media. The predominant organisms isolated from aluminum exchangers were species of Methylobacterium of which at least three colony morphologies and 11 distinct PFGE patterns we found; of the few bacteria isolated from the copper exchangers, the majority were species of Bacillus. The concentrations and type of bacteria recovered from the control, aluminum, exchangers were found to be dependent on the type of plating media used and were 11,411-47,257 CFU cm-2 per coupon surface. The concentration of fungi was found to average 378 CFU cm-2. Significantly lower concentrations of bacteria, 3 CFU cm-2, and fungi, 1 CFU cm-2, were recovered from copper exchangers regardless of the plating media used. Commonly used aluminum heat exchangers developed stable, mixed, bacterial/fungal biofilms in excess of 47,000 organisms per cm2 within 4 weeks of operation, whereas the antimicrobial properties of metallic copper were able to limit the microbial load affiliated with the copper heat exchangers to levels 99.97 % lower during the same time period.

Antimicrobial metallic copper surfaces kill Staphylococcus haemolyticus via membrane damage
Christophe Espírito Santo, Davide Quaranta, Gregor Grass. MicrobiologyOpen, Volume 1, Issue 1, pages 46–52, March 2012, DOI: 10.1002/mbo3.2

Molecular knowledge of the mode-of-action exerted by metallic Cu on microbes is certainly not strictly necessary for widespread application of antimicrobial surfaces in hygiene-sensitive areas. Currently, it is agreed-upon that genomic material will eventually degrade on metallic Cu (Weaver et al. 2011; Warnes and Keevil 2010; Espirito Santo and Grass, unpublished observations) but it is controversial if this process is causative for or subsequent to cell death (Weaver et al. 2010; Espirito Santo et al. 2011). We propose that current data favor the model that membranes are damaged first, causing lethality, followed by protein oxidation (Nandakumar et al. 2011) and DNA-degradation. In depth understanding of the sensitive cellular targets of Cu toxicity and the order of events leading to death, however, can be expected to provide new opportunities for improving the efficacy of Cu surfaces against microbes.

Evaluation of Antimicrobial Properties of Copper Surfaces in an Outpatient Infectious Disease Practice
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.

Antimicrobial activity of different copper alloy surfaces against copper resistant and sensitive Salmonella enterica
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.

Mechanism of Copper Surface Toxicity in Escherichia Coli O157:H7 and Salmonella Involves Immediate Membrane Depolarization Followed by Slower Rate of DNA Destruction which Differs from that Observed for Gram-positive Bacteria
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
We have reported previously that copper I and II ionic species, and superoxide but not Fenton reaction generated hydroxyl radicals, are important in the killing mechanism of pathogenic enterococci on copper surfaces.  In this new work we determined if the mechanism was the same in non-pathogenic ancestral (K12) and laboratory (DH5α) strains, and a pathogenic strain (O157), of Escherichia coli. The pathogenic strain exhibited prolonged survival on stainless steel surfaces compared with the other E. coli strains but all died within 10 min on copper surfaces using a 'dry' inoculum protocol (with approximately 10(7) cfu cm(-2) ) to mimic dry touch contamination. We observed immediate cytoplasmic membrane depolarization, not seen with enterococci or methicillin resistant Staphylococcus aureus, and loss of outer membrane integrity, inhibition of respiration and in situ generation of reactive oxygen species on copper and copper alloy surfaces that did not occur on stainless steel. Chelation of copper (I) and (II) ionic species still had the most significant impact on bacterial survival but protection by d-mannitol suggests hydroxyl radicals are involved in the killing mechanism. We also observed a much slower rate of DNA destruction on copper surfaces compared with previous results for enterococci. This may be due to protection of the nucleic acid by the periplasm and the extensive cell aggregation that we observed on copper surfaces. Similar results were obtained for Salmonella species but partial quenching by d-mannitol suggests radicals other than hydroxyl may be involved. The results indicate that copper biocidal surfaces are effective for Gram-positive and Gram-negative bacteria but bacterial morphology affects the mechanism of toxicity. These surfaces could not only help to prevent infection spread but also prevent horizontal gene transmission which is responsible for the evolution of virulent toxin producing and antibiotic resistant bacteria.
Control and Mitigation of Healthcare-Acquired Infections
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.

Antimicrobial Efficacy of Copper Alloy Furnishing in the Clinical Environment; a Cross-over Study
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.

Mechanism of Copper Surface Toxicity in Vancomycin-Resistant Enterococci following Wet or Dry Surface Contact
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.

The Role of Antimicrobial Copper Surfaces in Reducing Healthcare-associated Infections
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.

Risk Mitigation of Hospital Acquired Infections Through the Use of Antimicrobial Copper Surfaces
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.

Science, Technology and Design: Harnessing Copper’s Antimicrobial Power – A Review
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.

The potential for the application of metallic copper surfaces as a method for preventing surface and airborne microbial contamination in military healthcare facilities, food handling operations, and other occupational settings
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.

Bacterial Killing by Dry Metallic Copper Surfaces
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.

Metallic Copper as an Antimicrobial Surface
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.

Mechanisms of Contact-Mediated Killing of Yeast Cells on Dry Metallic Copper Surfaces
Davide Quaranta, Travis Krans, Christophe Espírito Santo, Christian G Elowsky, Dylan W Domaille, Christopher J Chang, Gregor Grass, Applied & Environmental Microbiology. Jan. 2011, p.416–426 Vol. 77, No. 2 0099-2240/11/$12.00 doi:10.1128/AEM.01704-10 ASM

Surfaces made of copper or its alloys have strong antimicrobial properties against a wide variety of microorganisms.  However, the molecular mode of action responsible for the antimicrobial efficacy of metallic copper is not known.  Here, we show that dry copper surfaces inactivate Candida albicans and Saccharomyces cerevisiae within minutes in a process called contact-mediated killing.

An evaluation of the antimicrobial properties of healthcare fomites (furnishings and equipment) made of copper alloys
T J Karpanen, A L Casey, P A Lambert, B D Cookson, P Nightingale, L Miruszenko, T S J Elliott. 7th International Conference of the Hospital Infection Society, Liverpool, October 2010.

Results presented at the 7th International Conference of the Hospital Infection Society in Liverpool, October 2010, confirm the role of antimicrobial copper touch surfaces as a supplement to routine cleaning to improve environmental hygiene in clinical environments.

The results showed that the highest contamination was found in the patient bathrooms, particularly on the chrome-plated toilet flush lever handles and tap handles, and on the plastic light pulls and toilet seats.

Copper-containing items, including door push plates, door pull handles, tap handles, toilet flush lever handles, patient over-bed tables, dressing trolleys, socket switches and light pull cord toggles - were found to have significantly fewer microorganisms on their surfaces than the controls and vancomycin-resistant enterococci, meticillin-sensitive Staphylococcus aureus and coliform bacteria were recovered less frequently from these.

Copper Surfaces Reduce the Microbial Burden in Out-Patient Infectious Disease Practice
B E Hirsch, H Attaway, R Nadan, S Fairey, J Hardy, G Miller, S Rai, D Armellino, M Schilling, W Moran, P Sharpe, A Estelle, J H Michel, H T Michels, M G Schmidt, Interscience Conference on Antimicrobial Agents and Chemotherapy, Boston, MA, 2010

Copper alloy surfaces are known to kill bacteria and decrease the environmental microbial bio-burden (MB) in ICUs. Out-patients share risk factors including co-morbidities, antibiotic exposure plus recent hospitalisation. The transient and high volume of potentially infectious and vulnerable subjects renders the out-patient clinic a significant locus of transmission that is often overlooked. This study shows the benefit of copper surfaces for their ability to reduce the MB in an infectious disease out-patient practice.  These findings support the clinical trial findings from Selly Oak, Calama and MUSC and, in addition, show a halo effect - reduced contamination in the vicinity of the copper surfaces. The calculated ratio of patients to the median burden enabled the conclusion to be drawn that use of the chair with the copper arm tops resulted in a 17-fold lower risk of exposure to environmental microbes than when patients used the standard chair.

Biocidal Efficacy of Copper Alloys against Pathogenic Enterococci Involves Degradation of Genomic and Plasmid DNA
S L Warnes, S M Green, H T Michels, C W Keevil, Appl. Environ. Microbiol. doi:10.1128/AEM.03050-09, 2010

The increasing incidence of nosocomial infections caused by glycopeptide-resistant enterococci is a global concern. Enterococcal species are also difficult to eradicate with existing cleaning regimes; they can survive for long periods on surfaces thus contributing to cases of reinfection and spread of antibiotic resistant strains. We have investigated the potential use of copper alloys as bactericidal surfaces. Clinical isolates of vancomycin-resistant Enterococcus faecalis and Enterococcus faecium were inoculated onto copper alloy and stainless steel surfaces. Samples were assessed for the presence of viable cells by conventional culture, detection of actively respiring cells and assessment of cell membrane integrity. Both species survived for up to several weeks on stainless steel. However, no viable cells were detected on any alloys following exposure for 1 hour at an inoculum concentration of ≤104 colony forming units per cm2. Analysis of genomic and plasmid DNA from bacterial cells recovered from metal surfaces indicates substantial disintegration of the DNA following exposure to copper surfaces that is not evident in cells recovered from stainless steel. The DNA fragmentation is so extensive, and coupled with the rapid cell death which occurs on copper surfaces, that it suggests mutation is less likely to occur. It is therefore highly unlikely that genetic information can be transferred to receptive organisms re-contaminating the same area. A combination of effective cleaning regimes and contact surfaces containing copper could be useful to not only prevent spread of viable pathogenic enterococci but also to mitigate against the occurrence of potential resistance to copper, biocides or antibiotics, and spread of genetic determinants of resistance to other species.

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.

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