Antimicrobial properties of copper

Materials World magazine
,
1 Apr 2006
Copper's antimicrobial properties could be employed to create hygienic surfaces in hospitals, such as doors, door knobs, counter tops and bed rails. Image: Nick Yarsley

Recent research undertaken at the University of Southampton, UK, has shown that copper surfaces could help to prevent the spread of Influenza A viruses that cause seasonal and epidemic flu infections. According to the UK's Department of Health, about 12,000 people die from such infections every year in the UK. 

Sponsored by the Copper Development Association Inc in the USA and the International Copper Association, the study was carried out by microbiology researchers Professor William Keevil and Dr Jonathon Noyce. They placed two million plaque-forming units (PFU) of Human Influenza A (H1N1) on samples of high purity copper (C11000) and on common stainless steel (S30400) at room temperature and then monitored the survival rates of the virus. On the stainless steel surface, the pathogen declined to one million PFUs after six hours, while on the copper surface only 500 PFUs remained after six hours - virtually eradicating the strain.

The Influenza A family of viruses also includes the Avian flu strain that has been causing concern worldwide. ‘Human Influenza A is near identical to the Avian Influenza (H5N1),' explains Keevil. ‘The H1 or H5 describes a minor change in the haemaglutinin binding protein on the virus surface that helps it to bind to blood cells'. He therefore believes that copper's antimicrobial properties should have the same effect on the Avian flu virus as it has on Human Influenza. ‘The findings are pertinent to the current concerns about containing a potential outbreak of the Avian flu strain.'

Copper on the counter 

Ongoing research conducted by Noyce and Keevil over the past 15 years has proved the significant antimicrobial effects of copper and its alloys. Among the organisms they inhibit or kill are E Coli O157:H7 in biofilms in drinking water systems or on dry work surfaces, and the superbug, MRSA (Methicillin-resistant Staphylococcus aureus), which is causing serious health concerns in hospitals. According to figures revealed by Keevil and Noyce in late 2005, MRSA survival on copper surfaces was only 1.5 hours and 4.5 hours on a brass surface. The copper-nickel-zinc surface resulted in significant and ongoing reduction in the pathogen after 4.5 hours, while on stainless steel the virus survived beyond 72 hours. The antimicrobial effect is seen at copper contents of between 63-99%.

Given these results, the UK's Copper Development Association (CDA) is keen to assert the possibility of using uncoated copper or high copper alloys in common-touch surfaces such as door knobs, push plates, counter tops, bed rails, and sinks, particularly in hospitals and other public facilities, to prevent cross contamination of infections. ‘Eighty per cent of infectious diseases are transmitted by touch', said Angela Vessey, Director of the CDA, at a seminar held in October 2005 in Birmingham, UK, on ‘Designing against Cross Infection'.

Keevil echos this opinion. ‘Stainless steel is actually rather inert. It is generally used because it is perceived as being easy to use and clean, and does not rust. However, pathogens can hide in the scratch marks and pits if the cleaning is not efficient and regular.' By contrast, he says, ‘Copper is an active surface that kills MRSA by inhibiting the respiration and also destroying the DNA. We believe that it probably has similar broad-spectrum properties for Influenza virus'. Tests have shown that a tarnished copper alloy surface can be just as effective.

The fact that copper alloys are durable, strong and ductile, and available in a range of colours makes them suitable replacements for materials such as stainless steel and aluminium in solid surfaces. Copper alloys can be formed into counter tops, cast into door handles, or drawn into tubes for grab rails. Similar antimicrobial efficacy to solid surfaces can also be achieved by infusing copper ions into fabrics, filters, or other materials, however, these ions would wash out and diminish in efficiency over time, explains Keevil. 

Disruptive influence 

But while it has long been recognised that copper has an ‘active' surface that can attack pathogens rapidly, the mechanics of this process have been studied for over 25 years and research is still ongoing. According to Keevil, it seems that the copper ions, and most likely the plus-two cupric ion, Cu+2, are able to ‘disrupt the function of microbial organisms in several ways. It is quite likely several of these mechanisms may be acting simultaneously. Effects range from induced disruption of the microbial cellular membrane functions, interference with protein activities, to inactivation and disruption of metabolic functions, and microbial death.' 

Keevil and Noyce hope to continue research in the area, identifying other important pathogens that can be controlled by copper surfaces, ‘not least because many pathogens are now resistant to a wide range of antibiotics'. Moreover, Keevil explains that viruses are difficult to control using vaccines, as they simulate host antibodies to target exposed cell surface structures, while copper attacks the whole structure of the virus. 

The antimicrobial properties of copper are currently employed in applications such as fungicides, antifouling paints and antimicrobial medicines. The CDA has developed the Antimicrobial Copper Interest Group to exploit copper's antimicrobial properties, and to promote them to architects, designers, product manufacturers, material suppliers, healthcare professionals, and facilities managers.

Members of the Group will be kept up-to-date on scientific research worldwide, the results of hospital trials in Japan, UK and Finland, and on regulatory issues and antimicrobial alloys.

 

Further information:

Copper Development Association