WHAT IS ANTIMICROBIAL?
An antimicrobial is an agent that kills microorganisms – bacteria, viruses and fungi (including moulds) – or inhibits their growth. Antimicrobials include antibiotics such as penicillin and disinfectants such as bleach (sodium hypochlorite). This resource describes the properties and applications of copper in solid form, as a surface material.
Laboratory tests have been developed to simulate contamination events under typical indoor temperature and humidity to measure the survival of bacteria on samples of copper and copper alloys such as brass and bronze.
This graph is the kill curve for MRSA on copper, brass (80% Cu, 20% Zn) and nickel silver (55% copper, 27% zinc and 18% nickel) at 20o C and typical indoor humidity. There is complete kill in less than 90 minutes on copper. The two copper alloys also showed good kill rates but the kill times were longer and dependent on copper content. Note that even after six hours, there is no reduction on the stainless steel coupon.
THE PROTECTIVE POWER OF COPPER EXPLAINED
Survival of Human Coronavirus 229E on Common Touch Surfaces and Copper
From prehistoric times, Copper has been known to inhibit growth of microbial organisms. It was used on boats to prevent buildup of molluscs and algae, used in the form of containers to keep water clean and as a roofing material which deterred the growth of moss, algae and lichen.
All these organisms are microbial in origin and the scientific knowledge now exists of how copper works to prevent not only these organisms, but also bacteria and viruses from persisting on surfaces such as door handles and handrails.
Viruses can survive on common surfaces for days or longer. This increases transmission and adds to infection rates. The use of copper reduces significantly this exposure risk by killing viruses left on surfaces quickly and safely.
Hand to mouth transmission is one of the leading routes to viral infection. Copper can offset this by simply killing viruses on surfaces commonly touched by hand.
Warnes SL, Little ZR, Keevil CW. 2015. Human coronavirus 229E remains infectious on common touch surface materials. mBio 6(6):e01697-15. Published American Society For Microbiology mBio Nov 10th 2015.
Having established the inherent ability of copper and copper alloys to eliminate bacteria and viruses in the laboratory, the next logical step was to discover how this would translate into real world environments and have practical application.
The first clinical trial was undertaken at Selly Oak Hospital in Birmingham, UK. The researchers replaced frequently-touched surfaces on a general medical ward – including over-bed tables, taps and door handles – with antimicrobial copper equivalents, measuring the contamination on these and comparing it with that on non-copper surfaces. The copper surfaces were found to have 90–100% fewer micro-organisms on them than the same items made from standard materials.
The surfaces identified as most contaminated were those closest to the patient:
Computer input devices (mouse/monitor bezel)
Visitor chair arms
Nurse call button
This graph shows the number of bacteria found on these components in the copper and control rooms. The copper items had 83% fewer bacteria than the control items. Of all the bacteria recovered, only 17% was from the copper items. The proposed standard for a safe level of bacteria in hospitals is shown as a horizontal line in orange at 250 cfu/100 cm2.
There were 58% fewer infections in the copper rooms than the control rooms. This result challenges current thinking that the environment only accounts for 20% of infections.
HOW DOES COPPER KILL BACTERIA?
Copper is an essential nutrient for bacteria as well as humans but, in high doses, copper ions can cause a series of negative events in bacterial cells. The exact mechanism by which copper kills bacteria is still unclear, however several processes exist and are being studied. One proposed sequence of events is given below:
A. Copper ions dissolved from the copper surface cause cell damage.
B. The cell membrane ruptures, leading to loss of the cell content.
C. Copper ions lead to the generation of toxic radicals that cause further damage.
D. DNA becomes degraded and leaves the cell.
WON'T MICROORGANISMS DEVELOP RESISTANCE TO COPPER?
As bacteria evolve resistance mechanisms to antibiotics, might resistance to copper develop? This is highly unlikely for three reasons:
Copper is naturally present in the Earth’s crust and, to date, no resistant organisms have been demonstrated. Copper-tolerant organisms do exist but even these die on contact with copper surfaces. In comparison, resistance to penicillin by certain bacterial species began to appear within 30 years of its introduction.
Copper kills microorganisms by multiple pathways rather than by acting in a specific way on one receptor like most antibiotics.
Microorganisms are killed before they can replicate, thus they cannot pass on genetic material that could ultimately lead to the development of resistance.