Copper and its alloys are natural antimicrobial materials. Ancient
civilizations exploited the antimicrobial properties of copper long
before the concept of microbes became understood in the nineteenth century. 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 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 efficacies
of copper alloy "touch surfaces" to destroy a wide range of microorganisms
that threaten public health. Mechanisms of antibacterial action of
copper 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 Laboratories 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.
Candida 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. 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.
Poliovirus is inactivated within 10 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 OH- 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. In inactivation experiments on the flu
strain, H1N1, which is nearly identical to the H5N1 avian strain and the 2009
H1N1 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 cells’ outer envelope.
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,
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, as well as others, are the subject of continuing
study by academic research laboratories around the world.
Antimicrobial efficacy of copper alloy touch surfaces
Copper alloy surfaces have intrinsic properties to destroy a wide range of
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 10 years regarding copper’s efficacy to destroy E. coli O157:H7,
methicillin-resistant Staphylococcus aureus, Staphylococcus, Clostridium
difficile, influenza A virus, adenovirus, and fungi. Stainless steel
was also investigated since it is such 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 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,
hemolytic uremic syndrome, 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. Over 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 demonstrate that this pathogen is
rapidly and almost completely killed within ninety minutes at room
temperature. At chill temperatures, over 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 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. Studies have been conducted to examine
the E. coli O157:H7 bactericidal efficacies on 25 different copper alloys
to identify those alloys that provide the best combination of antimicrobial
activity, corrosion/oxidation resistance, and fabrication properties.
Copper’s antibacterial effect was found to be intrinsic in all of the copper
alloys tested. As in previous studies, no antibacterial properties were
observed on stainless steel. Also, in confirmation with earlier studies the
rate of drop-off of E. coli O157:H7 on the copper alloys is faster at room
temperature than at chill temperature. For the most part, the bacterial kill
rate of copper alloys increased with increasing copper content of the alloy.
This is further evidence of copper’s intrinsic antibacterial properties.
Efficacy on brass, bronze, copper-nickel alloys
Brasses, which were frequently used for doorknobs and push plates in decades
past, also demonstrate bactericidal efficacies, but within a somewhat longer
time frame than pure copper. All nine brasses tested were almost completely
bactericidal at 20 °C within 60–270 minutes. Many brasses were almost
completely bactericidal at 4 °C within 180–360 minutes.
The rate of total microbial death on four bronzes varied from within 50–270
minutes at 20 °C, and from 180 to 270 minutes at 4 °C.
The kill rate of E. coli O157 on copper-nickel alloys increased with
increasing copper content. Zero bacterial counts at room temperature
were achieved after 105–360 minutes for five of the six alloys. Despite not
achieving a complete kill, alloy C71500 achieved a 4-log drop within the
six-hour test, representing a 99.99% reduction in the number of live
organisms. Efficacy on stainless steel
Unlike copper alloys, stainless steel does not exhibit any degree of
bactericidal properties. This material, which is one of the most common touch
surface materials in the healthcare industry, allows toxic E. coli O157:H7
to remain viable for weeks. Near-zero bacterial counts are not observed even
after 28 days of investigation. Epifluorescence photographs have
demonstrated that E. coli O157:H7 is almost completely killed on copper alloy
C10200 after just 90 minutes at 20 °C; whereas a substantial number of
pathogens remain on stainless steel S30400.
= MRSA = Methicillin-resistant Staphylococcus
aureus is a dangerous bacteria strain because it is resistant to beta-lactam
antibiotics. Recent strains of the bacteria, EMRSA-15 and EMRSA-16, are
highly transmissible and durable. This is of extreme importance to those
concerned with reducing the incidence of hospital-acquired MRSA infections.
In 2008, after evaluating a wide body of research mandated specifically by the
United States Environmental Protection Agency, registration approvals were
granted by EPA in 2008 granting that copper alloys kill more than 99.9% of
MRSA within two hours. Subsequent research conducted at the
University of Southampton compared the antimicrobial efficacies of copper and
several non-copper proprietary coating products to kill MRSA. At 20 °C, the
drop-off in MRSA organisms on copper alloy C11000 is dramatic and almost
complete within 75 minutes. However, neither a triclosan-based product nor
two silver-containing based antimicrobial treatments exhibited any
meaningful efficacy against MRSA. Stainless steel S30400 did not exhibit
any antimicrobial efficacy. In 2004, the University of Southampton
research team was the first to clearly demonstrate that copper inhibits MRSA.
On copper alloys — C19700, C24000, and C77000 — significant reductions in
viability were achieved at room temperatures after 1.5 hours, 3.0 hours
and 4.5 hours, respectively. Faster antimicrobial efficacies were associated
with higher copper alloy content. Stainless steel did not exhibit any
bactericidal benefits. = Clostridium difficile =
Clostridium difficile, an anaerobic bacterium, is a major cause of
potentially life-threatening disease, including nosocomial diarrheal
infections, especially in developed countries. C. difficile endospores can
survive for up to five months on surfaces. The pathogen is frequently
transmitted by the hands of healthcare workers in hospital environments. C.
difficile is currently a leading hospital-acquired infection in the UK,
and rivals MRSA as the most common organism to cause hospital acquired
infections in the US It is responsible for a series of intestinal health
complications, often referred to collectively as Clostridium difficile
Associated Disease. The antimicrobial efficacy of various
copper alloys against Clostridium difficile was recently evaluated. The
viability of C. difficile spores and vegetative cells were studied on copper
alloys C11000, C51000, C70600, C26000, and C75200. Stainless steel was used as
the experimental control. The copper alloys significantly reduced the
viability of both C. difficile spores and vegetative cells. On C75200, near
total kill was observed after one hour. On C11000, near total kill was observed
after 3 hours. On C70600, near total kill was observed after 5 hours. On
C26000, near total kill was achieved after 48 hours. On stainless steel, no
reductions in viable organisms were observed after 72 hours of exposure and
no significant reduction was observed within 168 hours.
= Influenza A = Influenza, commonly known as flu, is an
infectious disease from a viral pathogen different from the one that produces the
common cold. Symptoms of influenza, which are much more severe than the
common cold, include fever, sore throat, muscle pains, severe headache, coughing,
weakness and general discomfort. Influenza can cause pneumonia, which can
be fatal, particularly in young children and the elderly.
After incubation for one hour on copper, active influenza A virus particles were
reduced by 75%. After six hours, the particles were reduced on copper by
99.999%. Influenza A virus was found to survive in large numbers on stainless
steel. Once surfaces are contaminated with
virus particles, fingers can transfer particles to up to seven other clean
surfaces. Because of copper’s ability to destroy influenza A virus particles,
copper can help to prevent cross-contamination of this viral
pathogen. = Adenovirus =
Adenovirus is a group of viruses that infect the tissue lining membranes of
the respiratory and urinary tracts, eyes, and intestines. Adenoviruses
account for about 10% of acute respiratory infections in children.
These viruses are a frequent cause of diarrhea.
In a recent study, 75% of adenovirus particles were inactivated on copper
within 1 hour. Within six hours, 99.999% of the adenovirus particles were
inactivated. Within six hours, 50% of the infectious adenovirus particles
survived on stainless steel. = Fungi =
The antifungal efficacy of copper was compared to aluminium on the following
organisms that can cause human infections: Aspergillus spp., Fusarium
spp., Penicillium chrysogenum, Aspergillus niger and Candida albicans.
An increased die-off of fungal spores was found on copper surfaces compared
with aluminium. Aspergillus niger growth occurred on the aluminium coupons;
growth was inhibited on and around copper coupons.
See also Antimicrobial copper-alloy touch
surfaces Copper alloys in aquaculture
Medical uses of silver Oligodynamic effect
References