Antimicrobial properties of copper
Encyclopedia
Copper
and its alloys (brass
es, bronze
s, cupronickel
, copper-nickel-zinc, and others) 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 (i.e., no or little visible slime formation) 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.
and harmful microbes. Of the 312 citations mentioned in the review across the time period 1892–1973, the observations below are noteworthy:
A subsequent paper probed some of copper’s antimicrobial mechanisms and cited no less 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 cell
s and in the interstitial spaces between cells.
Examples of some of the molecular mechanisms noted by various researchers include the following:
Currently, researchers believe that the most important antimicrobial mechanisms for copper are as follows:
These potential mechanisms, as well as others, are the subject of continuing study by academic research laboratories around the world.
O157:H7, methicillin
-resistant Staphylococcus aureus
(MRSA), 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.
. The bacterium produces potent toxin
s that cause diarrhea, severe aches and nausea in infected persons. Symptoms of severe infections include hemolytic colitis (bloody diarrhea), hemolytic uremic syndrome (kidney disease), 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.
Results of E. coli O157:H7 destruction on an alloy containing 99.9% copper (C11000) demonstrate that this pathogen is rapidly and almost completely killed (over 99.9% kill rate) within ninety minutes at room temperature (20 °C). At chill temperatures (4 °C), 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 (including C10200, C11000, C18080, and C19700) 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 (UNS S30400). 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.
es, 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 (over 99.9% kill rate) 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 bronze
s 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.
(S30400) 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.
s. 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
(EPA), 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 (UK) 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 (over 99.9% kill rate) within 75 minutes. However, neither a triclosan-based product nor two silver-containing based antimicrobial treatments (Ag-A and Ag-B) 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 (99% copper), C24000 (80% copper), and C77000 (55% copper) — 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.
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 (99.9% copper), C51000 (95% copper), C70600 (90% copper), C26000 (70% copper), and C75200 (65% copper). Stainless steel (S30400) 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 (3 days) of exposure and no significant reduction was observed within 168 hours (1 week).
, 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.
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 (C11000) 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.
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.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and its alloys (brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
es, bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
s, cupronickel
Cupronickel
Cupronickel or copper-nickel or "cupernickel" is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Cupronickel is highly resistant to corrosion in seawater, because its electrode potential is adjusted to be neutral with regard to seawater...
, copper-nickel-zinc, and others) are natural antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...
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 (i.e., no or little visible slime formation) 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
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, algaeAlgae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
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 nigerAspergillus nigerAspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...
, Bacterium linens, Bacillus megateriumBacillus megateriumBacillus megaterium is a rod-shaped, Gram-positive, endospore forming, species of bacteria used as a soil inoculant in agriculture and horticulture.Bacterium is arranged into the streptobacillus form....
, Bacillus subtilisBacillus subtilisBacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...
, Brevibacterium erythrogenes, Candida utilis, Penicillium chrysogenumPenicillium chrysogenumPenicillium chrysogenum is common in temperate and subtropical regions and can be found on salted food products, but it is mostly found in indoor environments, especially in damp or waterdamaged buildings. It was previously known as Penicillium notatum. It has rarely been reported as a cause of...
, Rhizopus niveus, Saccharomyces mandshuricus, and Saccharomyces cerevisiaeSaccharomyces cerevisiaeSaccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
in concentrations above 10 g/L.
- Torulopsis 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 phosphoreumPhotobacterium phosphoreumPhotobacterium phosphoreum or Vibrio phosphoreum is a Gram-negative bioluminescent bacterium living in symbiosis with marine organisms. It can emit bluish-green light thanks to a chemical reaction between FMN, luciferin and molecular oxygen catalysed by an enzyme called Luciferase.- In Popular...
growth is inhibited by metallic copper.
- Paramecium caudatumParamecium caudatumParamecium caudatum are unicellular organisms belonging to the genus of Paramecium of the phylum Ciliophora. They they can reach 0.25mm in length and are covered with minute hair-like projections called cilia. The cilia are used in locomotion and feeding. They are often called slipper animalcules...
cell divisionCell divisionCell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
is reduced by copper plates placed on Petri dishPetri dishA Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
covers containing infusoria and nutrient media.
- PoliovirusPoliovirusPoliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is...
is inactivated within 10 minutes of exposure to copper with ascorbic acidAscorbic acidAscorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...
.
A subsequent paper probed some of copper’s antimicrobial mechanisms and cited no less 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 cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s 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 radicalRadical (chemistry)Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
s that inactivate viruses.
- Copper may disrupt enzymeEnzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
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 superoxideSuperoxideA superoxide, also known by the obsolete name hyperoxide, is a compound that possesses the superoxide anion with the chemical formula O2−. The systematic name of the anion is dioxide. It is important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature...
radicals. Repeated redoxRedoxRedox reactions describe all chemical reactions in which atoms have their oxidation state changed....
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 (swine flu) 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 enzymeEnzymeEnzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s to drive certain vital chemical reactions. Excess copper, however, can affect proteinProteinProteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s 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 peroxideHydrogen peroxideHydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
. Under these conditions, copper participates in the so-called Fenton-type reactionFenton's reagentFenton's reagent is a solution of hydrogen peroxide and an iron catalyst that is used to oxidize contaminants or waste waters. Fenton's reagent can be used to destroy organic compounds such as trichloroethylene and tetrachloroethylene ....
— 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 potassiumPotassiumPotassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
and glutamate. This leads to desiccationDesiccationDesiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
and subsequent cell death.
- While copper is needed for many protein functions, in an excess situation (as on a copper alloy surface), 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 heathcare 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. coliEscherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
O157:H7, methicillin
Methicillin
Meticillin or methicillin is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It should not be confused with the antibiotic metacycline.-History:Methicillin was developed by Beecham in 1959...
-resistant Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...
(MRSA), Staphylococcus
Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
, Clostridium difficile
Clostridium difficile
Clostridium difficile , also known as "CDF/cdf", or "C...
, influenza A virus, adenovirus
Adenoviridae
Adenoviruses are medium-sized , nonenveloped icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA genome...
, and fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
. Stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
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
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
, 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 (Advisory Committee on Dangerous Pathogens, UK) Hazard Group 3 foodborne and waterborne pathogenPathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
. The bacterium produces potent toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
s that cause diarrhea, severe aches and nausea in infected persons. Symptoms of severe infections include hemolytic colitis (bloody diarrhea), hemolytic uremic syndrome (kidney disease), 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 (C11000) demonstrate that this pathogen is rapidly and almost completely killed (over 99.9% kill rate) within ninety minutes at room temperature (20 °C). At chill temperatures (4 °C), 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 (including C10200, C11000, C18080, and C19700) 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 (UNS S30400). 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
BrassBrass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
es, 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 (over 99.9% kill rate) 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 bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
s 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 steelStainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
(S30400) 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 (MRSA) is a dangerous bacteria strain because it is resistant to beta-lactam antibioticBeta-lactam antibiotic
β-Lactam antibiotics are a broad class of antibiotics, consisting of all antibiotic agents that contains a β-lactam nucleus in its molecular structure. This includes penicillin derivatives , cephalosporins , monobactams, and carbapenems...
s. 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
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
(EPA), 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 (UK) 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 (over 99.9% kill rate) within 75 minutes. However, neither a triclosan-based product nor two silver-containing based antimicrobial treatments (Ag-A and Ag-B) 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 (99% copper), C24000 (80% copper), and C77000 (55% copper) — 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 (CDAD).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 (99.9% copper), C51000 (95% copper), C70600 (90% copper), C26000 (70% copper), and C75200 (65% copper). Stainless steel (S30400) 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 (3 days) of exposure and no significant reduction was observed within 168 hours (1 week).
Influenza A
InfluenzaInfluenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
, 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
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
, 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
AdenovirusAdenoviridae
Adenoviruses are medium-sized , nonenveloped icosahedral viruses composed of a nucleocapsid and a double-stranded linear DNA genome...
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 (C11000) 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 aluminiumAluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
on the following organisms that can cause human infections: Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...
spp., Fusarium
Fusarium
Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes, and are relatively abundant members of the soil microbial community. Some species produce mycotoxins in cereal crops that can affect human and animal health...
spp., Penicillium chrysogenum
Penicillium chrysogenum
Penicillium chrysogenum is common in temperate and subtropical regions and can be found on salted food products, but it is mostly found in indoor environments, especially in damp or waterdamaged buildings. It was previously known as Penicillium notatum. It has rarely been reported as a cause of...
, Aspergillus niger
Aspergillus niger
Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...
and Candida albicans
Candida albicans
Candida albicans is a diploid fungus that grows both as yeast and filamentous cells and a causal agent of opportunistic oral and genital infections in humans. Systemic fungal infections including those by C...
. An increased die-off of fungal spores was found on copper surfaces compared with aluminium. Aspergillus niger
Aspergillus niger
Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...
growth occurred on the aluminium coupons; growth was inhibited on and around copper coupons.