Copper, An Ancient Remedy Returning to Fight Microbial, Fungal and Viral Infections

Abstract

Copper has potent biocidal properties. Copper ions, either alone or in copper complexes, have been used for centuries to disinfect liquids, solids and human tissue. This manuscript reviews the biocidal mechanisms of copper and the current usages of copper and copper compounds as antibacterial, antifungal and antiviral agents, with emphasis on novel health related applications. These applications include the reduction of transmission of health-associated (nosocomial) pathogens, foodborne diseases, and dust mites loads and treatment of fungal foot infections and wounds. Possible future applications include filtration devices capable of deactivating viruses in solutions, such as contaminated blood products and breastmilk.

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272 Current Chemical Biology, 2009, 3, 272-278
1872-3136/09 $55.00+.00 © 2009 Bentham Science Publishers Ltd.
Copper, An Ancient Remedy Returning to Fight Microbial, Fungal and
Viral Infections
Gadi Borkow
*
and Jeffrey Gabbay
Cupron Scientific, Ligad Center 2, First Floor, Rechov HaMa'ayan 4, Modiin 71700, Israel
Abstract: Copper has potent biocidal properties. Copper ions, either alone or in copper complexes, have been used for
centuries to disinfect liquids, solids and human tissue. This manuscript reviews the biocidal mechanisms of copper and the
current usages of copper and copper compounds as antibacterial, antifungal and antiviral agents, with emphasis on novel
health related applications. These applications include the reduction of transmission of health-associated (nosocomial)
pathogens, foodborne diseases, and dust mites loads and treatment of fungal foot infections and wounds. Possible future
applications include filtration devices capable of deactivating viruses in solutions, such as contaminated blood products
and breastmilk.
Keywords: Copper, biocide, fungicide, antiviral, acaricidal, nosocomial infections, wound healing.
INTRODUCTION
Copper has been used as a biocide for centuries [1]. In
ancient Egypt (2000 BC), copper was used to sterilize water
and wounds. The ancient Greeks in the time of Hippocrates
(400 BC) prescribed copper for pulmonary diseases and for
purifying drinking water. Gangajal, “Holy water”, given to
Hindu devotees to drink as a blessed offering, is stored in
copper utensils as it keeps the water sparkling clean. During
the Roman Empire, copper cooking utensils were used to
prevent the spread of disease. The early Phoenicians nailed
copper strips to ships’ hulls to inhibit fouling and thus in-
crease speed and maneuverability. The Aztecs used copper
oxide and malachite for treating skin conditions. Early
American pioneers moving west across the American conti-
nent put copper coins in large wooden water casks to provide
safe drinking water for their long journey. By the 18th cen-
tury, copper had come into wide clinical use in the Western
world in the treatment of lung and mental disorders. In the
Second World War, Japanese soldiers put pieces of copper in
their water bottles to help prevent dysentery. Copper sul-
phate was (and is still) highly prized by some inhabitants of
Africa and Asia for healing sores and skin diseases.
Were all these civilizations right in using copper for the
above mentioned purposes? Indeed they were! The following
sections review scientific studies demonstrating the potent
biocidal properties of copper and copper compounds and
their current uses in health related applications.
COPPER BIOCIDAL ACTIVITIES
The wide use of copper due to its antifungal properties
started in 1761, when it was discovered that seed grains
soaked in copper sulphate inhibited seed-borne fungi. Within
a few decades, the practice of treating seed grains with cop-
per sulphate had become so general and effective that today
seed-borne fungi are no longer of any economic importance.
*Address correspondence to this author at the Cupron Scientific, Ligad
Center 2, First Floor, Rechov HaMa'ayan 4, Modiin 71700, Israel;
E-mail: gadi@cupron.com
In the 1880s a mixture of copper sulphate, lime and water
(called “Bordeaux mixture") and a mixture of copper sul-
phate and sodium carbonate (called “Burgundy mixture”)
became the fungicide of choice in the U.S. and France, re-
spectively, for spraying grapes and vines to fight mildew.
The fungicidal properties of copper were demonstrated in
controlled laboratory studies starting in the early 1950s (e.g.
[2-4]) and since then copper and copper compounds have
been shown to effectively kill a wide range of yeast and
fungi such as Aspergillus carbonarius [5]; Aspergillus fumi-
gatus [6]; Aspergillus niger [6-8]; Aspergillus oryzae [7];
Candida albicans [6,8-13]; Cryptococcus neoformans [6];
Epidermophyton floccosum [6]; Microsporum canis [6]; My-
rothecium verrucaria [7]; Saccharomyces cerevisiae [14,15];
Torulopsis pintolopesii [9]; Trichoderma viride [7]; Tricho-
phyton mentagrophytes [7,8,13] and Tricophyton rubrum
[6,13]. Thus, copper fungicides have become indispensable
and many thousands of tons are used annually all over the
world in agriculture [16,17]. For example, copper sulphate
and copper hydroxide are employed for the control of downy
mildew on grapes and green slime in farm ponds, rice fields,
irrigation and drainage canals, rivers, lakes and swimming
pools [17]. However, copper compounds may be very toxic
to fish and other organisms. The environmental hazards re-
sulting from copper build-up in sediments and the need for
high dosages have led to a constant search for and produc-
tion of compounds that provide the copper in a chelated form
(e.g. [18-20]). Chelated copper is non-reactive with other
chemical constituents in the water. For example, the copper
water-insoluble compound, copper-8-quinolinolate and some
of its derivates [7] are used in fruit-handling equipment. This
compound is also used to reduce environmental contamina-
tion of fungi in hospitals at concentrations above 0.4 g/ml
[16], since infection with fungi, such as Aspergillus spp, is a
major problem among immunocompromised patients, such
as AIDS patients.
Copper sulphate has been in use since 1838 for preserv-
ing timber and is today the base for many proprietary wood
preservatives [21]. Copper is also used as the active ingredi-
ent in products that prevent roof moss formation, such as

Copper Fighting Microbial, Fungal and Viral Infections Current Chemical Biology, 2009, Vol. 3, No. 3 273
copper granules found in 3M Scotchgard™ Algae Resistant
Roofing System [22]. Interestingly, the growth of barnacles,
seaweed, tubeworms, and other organisms on boat bottoms
produces surface roughness that increases turbulent flow,
acoustic noise, drag, and fuel consumption. An average in-
crease of 10 m in hull roughness can result in a 1% increase
in fuel consumption! This has led to the painting of boat bot-
toms with copper-containing paints that reduce fouling and
microbial biofilm formation in ships and save energy [23],
and now copper is quite commonly used in antifouling paints
[23-25].
Several copper compounds, such as copper sulphate,
copper nitrate and cupric chloride-bis-n-dodecylamine, are
potent molluscicides. For example, the following snails have
been shown to be killed by these compounds: Biomphalaria
glabrata [26]; Biomphalaria alexandrina [27-29] and Lym-
naea natalenesis [28,29]. Control of snails may be an impor-
tant strategy in fighting some human diseases, such as bil-
harziasis. This disease is caused by a trematode parasite,
Schistosoma mansoni, which uses snails and humans as
hosts.
The recognition that copper has potent antibacterial prop-
erties followed and was well established in laboratory studies
(for a recent review see reference [30]). Some examples in-
clude the killing by means of copper or copper compounds
of Acinetobacter calcoaceticus/baumannii [31,32]; Bacillus
subtilis [32,33]; Bacillus macerans [34]; Campylobacter
jejuni [35]; Citrobacter [32]; Clostridium difficile [36,37];
Enterococci [11,12]; Escherichia coli [10-12,32,33,38-41];
Legionella pneumophila [31,42,43]; Listeria monocytogenes
[12,44-46]; Klebsiella pneumoniae [32]; Mycobacterium
tuberculosis [47]; Pseudomonas aeruginosa [48]; Pseudo-
monas fluorescens [45]; Pseudomonas striata [34]; Salmo-
nella sp. [12,32,35,39]; Salmonella typhimurium [45,49];
Shewanella putrefaciens [45]; Shigella flexnerii [32];
Staphylococcus epidermidis [50]; Staphylococcus aureus
[10-12,31-33,41,45,46,51,52]; and Streptococcus [32,53].
Recent studies have demonstrated that non-soluble copper
compounds, such as glass coated with thin films of CuO
[54], degradable phosphate glass fibres impregnated with
CuO [50,53] or metallic and copper alloys
[35,36,38,40,44,47,51,55,56] have potent biocidal properties,
even against difficult bacterial spores [36]. Interestingly,
bacteria exposed to metallic copper surfaces do not enter a
viable but nonculturable physiological state, in which they
are viable but do not multiply, but are completely inactivated
[44]. Importantly, based on the vast amount of antimicrobial
efficacy testing (180 tests, utilizing 3235 control and test
samples, conducted in independent microbiology laborato-
ries) sponsored by the Copper Development Association
(CDA), the U.S. Environmental Protection Agency (EPA)
has recently (March 2008) approved the registration of cop-
per alloys as materials with antimicrobial properties, thus
allowing the CDA to make public health claims [57]. The
following statement is included in the registration: "When
cleaned regularly, antimicrobial copper alloys surfaces kill
greater than 99.9% of bacteria within two hours, and con-
tinue to kill more than 99% of bacteria even after repeated
contamination". These public health claims acknowledge
that copper, brass and bronze are capable of killing harmful,
potentially deadly bacteria, such as Methicillin-resistant S.
aureus (MRSA). MRSA is one of the most virulent strains of
antibiotic-resistant bacteria and a common cause of hospital-
and community-acquired infections. Copper is the first solid
surface material to receive this type of EPA registration.
Copper demonstrates potent antiviral (virucidal) activity
as well. The inactivation of the following enveloped or
nonenveloped, single- or double-stranded DNA or RNA vi-
ruses by copper and copper compounds, has been reported:
bacteriophages [58-62], Infectious Bronchitis Virus [63],
Poliovirus [61,64], Junin Virus [59], Herpes Simplex Virus
[58,59], Human Immunodeficiency Virus Type 1 (HIV-1)
[11,65-67], West Nile Virus [11], Coxsackie Virus Types B2
& B4, Echovirus 4 and Simian Rotavirus SA11 [68]. More
recently, the inactivation of Influenza A [55,65], Rhinovirus
2, Yellow Fever, Measles, Respiratory Syncytial Virus,
Parainfluenza 3, Punta Toro, Pichinde, Adenovirus Type 1,
Cytomegalovirus and Vaccinia [65] has been demonstrated.
BIOCIDAL MECHANISMS OF COPPER
Copper exerts its toxicity to microorganisms through
several parallel mechanisms, which eventually may lead to
the microorganisms’ death even within minutes of their ex-
posure to copper (e.g. [14,38,65]). It is likely that the first
site that copper damages is the microorganisms’ envelope.
Recently, Nan Li and his colleagues [69], by using atomic
force microscopy, force-distance curves and inductively
coupled plasma mass spectrometer tests, studied the effects
of austenitic (a solid solution of ferric carbide or carbon in
iron) stainless steel containing or not containing copper on
the plasma membrane of E. coli. They found that the copper
containing steel adhered to the bacteria plasma membrane,
via the electrostatic forces exerted by Cu
2+
, to a significantly
greater extent than the austenitic stainless steel not contain-
ing copper. They reported that initial damage occurred to the
lipopolysaccharide patches on the outer plasma membrane,
which collapsed while the inner part of the bacteria remained
intact. Already in 1988, Ohsumi and colleagues reported that
Cu
2+
elicits significant permeability changes in intact Sac-
charomyces cerevisiae cells [14], which depending on the
plasma membrane fatty acid composition and the membrane
permeability, increased markedly in cells enriched with
polyunsaturated fatty acids [70]. Extensive copper-induced
disruption of membrane integrity inevitably leads to loss of
cell viability. However, even relatively small alterations in
the physical properties of biological membranes can elicit
marked changes in the activities of many essential mem-
brane-dependent functions, including transport protein activ-
ity and ion permeability [71].
While copper may interact with many microbial proteins
without damaging them, such as with copper chaperones
(e.g. [72,73]), copper may damage many proteins, both on
the microorganism envelope or within the cell, especially
when found in high concentrations, above the threshold by
which many microorganisms can cope with excess copper.
This may occur via displacement of essential metals from
their native binding sites in the proteins, or via direct interac-
tions with the proteins. In both cases, conformational
changes in the protein structure or in the protein active site
may occur, resulting in the inhibition or neutralization of the
protein biological activities. For example, specific oxidation
of the cysteine in the active site of vaccinia H1-related pro-
tein tyrosine phosphatase by Cu
2+
results in complete inacti-

274 Current Chemical Biology, 2009, Vol. 3, No. 3 Borkow and Gabbay
vation of the protein activity [74]. Another example is the
neutralization of HIV-1 protease, an essential protein for the
replication of the virus, by stoichiometric concentrations of
copper ions [75]. Direct inhibition by Cu
2+
required the pres-
ence of cysteine residue(s) in the protease [75,76]. Copper
also may mediate free radical attack of amino acids, espe-
cially of histidine and proline, causing substantial protein
alterations and even protein cleavage [77,78].
Copper ions can also damage nucleic acids. By cross
linking within and between strands of DNA [79] copper may
cause helical structure disorders and DNA denaturation [80].
In single-stranded DNA, such as that found in many DNA
viruses, a copper binding site was found on average in every
three nucleotides [81]. Guanine-specific covalent binding of
Cu
2+
in double stranded DNA was demonstrated following
crystallization (1.2-A resolution) of DNA soaked with cupric
chloride [82], explaining the observed specificity of Cu
2+
-
induced oxidative DNA damage that occurs near guanine
residues [83]. It has been suggested that subsequent to the
specific binding of copper to deoxyribonucleic acids, re-
peated cyclic redox reactions generate several OH radicals
near the binding site causing multiple damage to the nucleic
acids [84]. When examining the effects of Cu
2+
on purified
S. typhimurium DNA, DNA breakage occurred only when
the copper ions and H
2
O
2
were present, while no damage to
the DNA was detectable after incubation with the metal ions
alone or with H
2
O
2
alone [49], supporting the notion that
copper catalyzes the conversion of H
2
O
2
to hydroxyl radicals
[85], at least in vitro. Although copper binds DNA in vitro,
stronger competing ligands, such as glutathione and cysteine
[86,87], may remove copper away from the DNA in vivo.
Furthermore, recent studies using E. coli lacking copper ex-
port genes indicate that copper does not catalyze significant
oxidative DNA damage in vivo [86]. Electron paramagnetic
resonance spin trapping assays showed that the majority of
H
2
O
2
-oxidizable copper was located in the periplasm, away
from the DNA. However, it still may be that in some micro-
organisms, especially in viruses, copper oxidative damage to
the genetic material may occur through Fenton mechanisms.
Indirect toxic mechanisms have been suggested. For exam-
ple, exposure to high concentrations of copper may increase
the rate of H
2
O
2
generation [88], which could have acceler-
ated iron-mediated oxidative DNA damage [86].
In general, the redox cycling between Cu
2+
and Cu
1+
,
which can catalyze the production of highly hydroxyl radi-
cals, with subsequent damage to lipids, proteins, DNA and
other biomolecules [30,89], makes copper reactive and a
particularly effective antimicrobial. Other closely related
metals, such as zinc and nickel, do not readily undergo re-
dox-cycling reactions and are more stable in their various
cationic states. Zinc, which is an essential trace metal like
copper and well metabolized by humans, displays antifungal
properties [90]. Zinc pyrithione, for example, is widely used
as an antifouling agent in paints [91]. However, free zinc ion
in solution is highly toxic to plants, invertebrates, and even
to vertebrate fish [92] and in high dosage can promote oxida-
tive toxicity in humans [93]. Nickel, which also has potent
antimicrobial properties, is a known haematotoxic, immuno-
toxic, neurotoxic, genotoxic, nephrotoxic, hepatotoxic and
carcinogenic agent [94] and is therefore not used.
Many bacteria and fungi have different mechanisms to
deal with excess copper (reviewed in [30]). These include
exclusion by a permeability barrier, intra- and extra-cellular
sequestration by cell envelopes, active transport membrane
efflux pumps, reduction in the sensitivity of cellular targets
to copper ions, extracellular chelation or precipitation by
secreted metabolites including copper, and adaptation and
tolerance via upregulation of necessary genes in the presence
of copper (e.g. [95,96]). However, above a certain threshold
and time of exposure, which differs between the microorgan-
isms, they cannot deal with the copper overload and die. Due
to the multisite kill mechanism of copper and mostly non-
specific mechanisms of damage exerted by copper (see
above and [30]), their tolerance to copper is relatively low,
as compared to the resistance to antibiotics demonstrated by
some microorganisms (i.e., 10 fold lower sensitivity to cop-
per as opposed to 1000 fold less sensitivity to methicillin, for
example by methicillin resistant S. aureus). Thus, in contrast
to the highly resistant microbes that have evolved to antibiot-
ics in less than 50 years of use, tolerant microbes to copper
are extremely rare even though copper has been a part of the
earth for millions of years. Viruses do not have tolerance and
repair mechanisms, such as DNA repair mechanisms, as bac-
teria and fungi and thus are highly susceptible to copper in-
duced damage.
COPPER HEALTH RELATED APPLICATIONS
In contrast to the high susceptibility of microorganisms
to copper [30], copper is considered safe to humans, as dem-
onstrated by the widespread and prolonged use by women of
copper intrauterine devices [97-100]. The risk of adverse
reactions due to dermal contact with copper is considered
extremely low [101,102]. Copper is an essential trace ele-
ment involved in numerous human physiological and meta-
bolic processes [103,104], including in wound repair [105],
and many over-the-counter treatments for wound healing
contain copper [106,107]. The National Academy of Sci-
ences Committee established the U.S. Recommended Daily
Allowance of 0.9 mg of copper for normal adults [108].
Copper and copper-based compounds, due to their potent
biocidal properties, are now routinely used in several health-
related areas. These include 1) control of Legionella
[42,43,109-111] and other bacteria [112] in hospital water
distribution systems. Hospital-acquired Legionnaires' disease
has been reported from many hospitals since the first out-
break in 1976. Although cooling towers were linked to the
cases of Legionnaires' disease in the years after its discovery,
potable water has been the environmental source for almost
all reported hospital outbreaks [110,113]. Copper-silver ioni-
sation systems have emerged as the most successful long-
term disinfection method for hospital water disinfection sys-
tems [42,43,109-111]; 2) prevention of algae and other para-
sites growth in potable water reservoirs (e.g. [114,115]). The
efficacy of silver/copper/chlorine combinations in drinking
water for inactivation of protozoa such as Hartmannella
vermiformis and Naegleria fowleria [responsible for primary
amoebic meningoencephalitis] amoebas and Tetrahymena
pyriformis, is being explored [116,117]; 3) reduction of car-
ies in dentistry. Dental cements containing copper have been
shown to have antimicrobial and anticariogenic properties
[118,119]; 4) reduction of foodborne diseases through the
production and use of self-sterilizing metallic copper sur-

Copper Fighting Microbial, Fungal and Viral Infections Current Chemical Biology, 2009, Vol. 3, No. 3 275
faces [35,40,44,56] or materials containing copper
[11,12,53,54,120], in which the food is kept, handled or
transported. The addition of copper to drinking glasses has
been shown to reduce biofilm formation of Streptococcus
sanguis, thus reducing the risk of oral infections [53]. The
USA Centers for Disease Control (CDC) reported in 1999
that 76 million Americans (~25% of the population) suffer
from food poisoning annually. Recently they reported that
while several foodborne illnesses - yersinia, shigella, listeria,
sampylobacter, and shiga toxin-producing E. coli 0157 -
have become somewhat less common than they were in
1999, the overall rate of reported foodborne illness hasn't
budged much since 2004; and 5) in birth control by using
copper intrauterine contraceptive devices [100,121].
Novel uses of copper or copper-based compounds in
health-related applications are being explored and/or imple-
mented. One area is the reduction of transmission of health-
associated (nosocomial) pathogens in hospitals, clinics and
elderly homes, by i) making hospital hard surfaces, like door
knobs, bed rails, and intravenous stands, with metallic cop-
per [36,47,51,55] ii) making hospital soft surfaces, like
sheets, patient robes, patient pajamas, and nurse clothing,
from copper-impregnated biocidal textiles [11,12,122], and
iii) disinfecting contaminating cloths with copper-based bio-
cides [31].
Dust mites are considered to be an important source of
allergen for perennial rhinitis and asthmatic attacks [123].
Recently it was demonstrated that copper-impregnated fab-
rics are acaricidal [8,11]. Thus, elimination of house dust
mites in mattresses, quilts, carpets and pillows may improve
the quality of life of those suffering from dust-mite related
allergies.
The use of copper-impregnated socks for the prevention
and treatment of fungal foot infections (athlete’s foot) has
been reported [13,124]. Similarly, the use of copper oxide
containing wound dressings for the reduction of dressing and
wound contamination has shown excellent results in human
and animal studies, not only in reducing the contamination of
the wounds, but more importantly in enhancing and allowing
wound repair, especially of diabetic ulcers in which conven-
tional treatment modalities failed in closing the wounds (un-
published data).
A possible application of copper due to its potent viruci-
dal properties is its use in filtration devices that can deacti-
vate viruses in contaminated solutions, such as contaminated
blood products and breastmilk. Recently the deactivation of
HIV-1 and other viruses in suspension by copper-based fil-
ters has been reported [65,66].
The capacity to impregnate copper into different textile
products, as well as into latex and other polymeric materials
[10-12] allows for the production of personal protective
equipment (PPE) with antimicrobial and antiviral properties
to be used by first responders and laboratory personnel, who
may be exposed to pathogens. PPE such as gloves, masks
and disposable robes, may increase the safety not only of
those using these products but of the immediate environment
and assure safer disposal of the used items. Similarly, police
or health-workers uniforms that may be exposed to contami-
nated solutions, such as blood, would reduce the risk of
pathogens transmission.
In contrast to the above copper health related applica-
tions, copper is not appropriate for use for systemic infec-
tions, mainly since once copper is ingested it readily inter-
acts with transport proteins as well as small molecular
weight ligands [125,126], making it unavailable as an antim-
icrobial. Furthermore, in cases where no efficacious copper
metabolism occurs, the unligated free copper in the body
may be involved in disease pathogenesis, such as in Alz-
heimer's disease [127]. Another limitation of copper may be
the price of copper, which has recently escalated. However,
this is of special relevance mainly when whole surfaces or
products are made with copper or copper alloys. It is signifi-
cantly less prohibitive when copper compounds, such as
copper oxide, are impregnated in low percentages in medical
devices or other health related products. In any case, when
compared to the alternatives or the consequences of not us-
ing copper-containing products, e.g., increased nosocomial
infections and food poisoning and the related costs of treat-
ments, the issue of the copper cost is not significant.
In conclusion, the safety of copper to humans and its po-
tent biocidal properties allow the use of copper in many ap-
plications (Fig. (1)), including several that address medical
concerns of the greatest importance. While some of these
applications are already being amply used, novel possible
applications of copper may have a major effect on our lives.
CONFLICT OF INTEREST
G.B. is the Chief Medical Scientist of Cupron. J.G. is the
CEO of Cupron. Cupron is a company that uses copper oxide
in its medical and consumer applications.
ABBREVIATIONS
CDA = Copper Development Association
EPA = U.S. Environmental Protection Agency
Fig. (1). Current and future potential applications of copper and
copper compounds in different areas, which are based on copper’s
biocidal properties.

276 Current Chemical Biology, 2009, Vol. 3, No. 3 Borkow and Gabbay
MRSA = Methicillin-resistant Staphylococcus aureus
HIV-1 = Human Immunodeficiency Virus Type 1
PPE = Personal protective equipment
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Received: December 18, 2008 Revised: April 08, 2009 Accepted: April 24, 2009