ANTIMICROBIAL COPPER

Before it was recognized that microorganisms existed, citizens of the early Roman Empire used copper piping to improve public hygiene. They observed that water delivered through copper was safe to drink and that copper utensils and cookware helped to prevent the spread of disease.

Much later, after microbes were discovered and the germ theory of infection linked bacteria and other microorganisms to infection and disease, scientists began to understand how copper’s antimicrobial properties could be harnessed to provide additional benefits. Today, the antimicrobial uses of copper have been expanded to include fungicides, pesticides, antifouling paints, antimicrobial medicines, oral hygiene products, hygienic medical devices, antiseptics and a host of other useful applications.

Several bacteria, known to be human pathogens, die when placed on copper alloy surfaces. Many bacteria have been tested including: E. coli O157:H7 and Listeria monocytogenes, both food-borne pathogens associated with several large-scale food recalls, Methicillin-Resistant Staphylococcus aureus (MRSA), a serious hospital-acquired infection and L. pneumophila, a principal agent of Legionnaire’s disease.The concentration of live bacteria drops from several orders of magnitude to zero on copper alloys in a few hours. In marked contrast, no reduction is seen in the concentration of live organisms on other metals such as stainless steel during a six-hour test period. Copper alloys tested include high coppers, brasses, bronzes, copper -nickels and copper-nickel-zincs. In studies, the inhibition effects of a given alloy on E. coli, for example, decreases, as temperatures decrease from 20°C to 4°C. In general, the inhibition effects decrease as copper content of the alloys decreases. Many results suggest the selection of copper alloys for surfaces exposed to human touch or food contact. Using copper alloys in this manner can materially assist in reducing the transmission of potentially infectious organisms.

A more detailed description of a study regarding copper and L. pneumophila: Much is known about the antimicrobial effects of copper in the inactivation of L. pneumophila, a principal agent of Legionnaire’s disease.Legionnaires’ disease is an acute fulminating pneumonia with a low attack rate but causing approximately 12% fatalities and has been ranked as the second or third most frequent cause of pneumonia requiring hospitalization. Water systems are neither designed nor maintained to be sterile and can become colonized with legionellae. This can lead to a potential public health hazard if the legionellae proliferate. The resistance of Legionella to chlorine is further enhanced by inclusion of the organisms in amoebae or by growth in biofilms (Kuchta et al., 1993). It is unsurprising, therefore, that legionellae have repeatedly been found in chlorinated water that complies with microbiological standards for drinking water. Alternative treatment barriers have included use of UV irradiation, monochloramine, ozone and metal ionization (copper and silver), with varying success, depending on the type of engineered system. Investigations regarding the antimicrobial properties of copper versus aluminum, steel, plastics and other building materials have been conducted for some time. In early experiments, dissolved copper and copper surfaces were shown to inhibit nonpathogenic strains of E. coli and ACDP Category 2/3 pathogens, such as Legionella pneumophilia. Plastic and stainless steel surfaces, on the other hand, did not inhibit the growth of these microorganisms. Using a highly reproducible laboratory model of a potable water supply, researchers demonstrated that biofilms of high species diversity could be generated reproducibly for many months on a range of plastic and metal materials. L. pneumophila was able to colonize these materials, which are commonly used in cold or warm potable water supplies, including mild steel, stainless steel, polypropylene, polyethylene, unpolymerized polyvinyl chloride (UPVC), chlorinated polyvinyl chloride (CPVC) and the jointing compounds, latex and ethylene-propylene copolymer. Moreover, L. pneumophila could survive and grow in the biofilms, even at temperatures up to 50°C on plastic surfaces but not copper. These researchers also found that E. coli O157, in a desiccated state, survived on stainless steel for extended periods at chill and room temperatures. At 20ºC, VTEC organisms were observed at 34 days. At 4ºC, organisms were observed for up to 60 days.These results clearly confirmed that stainless steel is a potential source of cross contamination, unless it is disinfected every day. Copper, on the other hand, inactivated the VTEC organisms in just 4 hours at 20ºC and in 14 hours at the chill temperature of 4ºC. Brass (Muntz metal alloy consisting of 60% Cu + 40% Zn) inactivated the bacteria in 4 days at 20ºC and in 12 days at 4ºC.

Why Does This All Happen?: The ways in which copper acts on microorganisms is a complicated subject, and beyond the scope of this introduction. However, a few of the many proposed mechanisms include :
~If proteins are complexed or altered, they can no longer perform their normal functions.
~Copper complexes form radicals (that inactivate viruses).
~Metals, such as copper, may disrupt enzyme structure.
~Inactivation is due to oxidation potential of the ion.
~Transition metals (including copper) facilitate deleterious activity in superoxide radicals.
~Cu+2 can form protein chelates through a protein’s carboxylate and amino groups, thereby inactivating a protein.
~Divalent cations, such as Cu+2, may strain protein structure, causing hydrogen bonds within the DNA to break, and thus opening the double helix.
~If the nucleic acid helix is stabilized or destabilized by chelation with a metal ion, replication or transcription is altered, thereby rendering the microorganism inactive.
~Cu+2 has a specific affinity for DNA and can bind and disorder helical structures by crosslinking within and between DNA strands.
~Cu+2 may complex messenger RNA (and thereby play a role in disinfection of viruses).
~Cu+2 has a strong affinity for O-, N- and S- sites in proteins.
~Disinfection due to metal complexes is important in enabling a possible entry through a cells membrane.
~Copper can interact with lipids, causing their peroxidation and opening holes in the cell membrane.
~Studies on copper-injured E. coli cells indicate that the respiratory chain is damaged at least one site and is associated with impaired cellular metabolism.


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