Metallic Copper as an Antimicrobial Surface

ABSTRACT Bacteria, yeasts, and viruses are rapidly killed on metallic copper surfaces, and the term “contact killing” has been coined for this process. While the phenomenon was already known in ancient times, it is currently receiving renewed attention. This is due to the potential use of copper as an antibacterial material in health care settings. Contact killing was observed to take place at a rate of at least 7 to 8 logs per hour, and no live microorganisms were generally recovered from copper surfaces after prolonged incubation. The antimicrobial activity of copper and copper alloys is now well established, and copper has recently been registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material. In several clinical studies, copper has been evaluated for use on touch surfaces, such as door handles, bathroom fixtures, or bed rails, in attempts to curb nosocomial infections. In connection to these new applications of copper, it is important to understand the mechanism of contact killing since it may bear on central issues, such as the possibility of the emergence and spread of resistant organisms, cleaning procedures, and questions of material and object engineering. Recent work has shed light on mechanistic aspects of contact killing. These findings will be reviewed here and juxtaposed with the toxicity mechanisms of ionic copper. The merit of copper as a hygienic material in hospitals and related settings will also be discussed.

The use of copper by human civilizations dates back to between the 5th and 6th millennia B.C. It was the first metal used, presumably because it could be found in a native, metallic form which did not require smelting. Its use remained scattered throughout Europe and the Middle East, and the archeological evidence remains scarce. With the invention of smelting, the metallurgic age began and the advantage of combining copper with tin to form bronze was discovered. The earliest bronze artifacts originated from the Middle East and China and date to before 3000 B.C., but it was not until the second millennium B.C. that bronze was used throughout Europe. The ability to smelt and forge iron from about 1000 B.C. marks the end of the Bronze Age and the beginning of the Iron Age. The oldest recorded medical use of copper is mentioned in the Smith Papyrus, one of the oldest books known (8). This Egyptian medical text, written between 2600 and 2200 B.C., describes the application of copper to sterilize chest wounds and drinking water (8). Greeks, Romans, Aztecs, and others also used copper or copper compounds for the treatment of such ailments as headaches, burns, intestinal worms, and ear infections and for hygiene in general. In the 19th century, a new awareness of copper's medical potency was spawned by the observation that copper workers appeared to be immune to cholera in the 1832 and subsequent outbreaks in Paris, France (8). The use of copper in medicine became widespread in the 19th and early 20th centuries, and a variety of inorganic copper preparations were used to treat chronic adenitis, eczema, impetigo, scrofulosis, tubercular infections, lupus, syphilis, anemia, chorea, and facial neuralgia (8). The use of copper as an antimicrobial agent continued until the advent of commercially available antibiotics in 1932. The spread of antibiotic resistance through selective pressure began and today has made antibiotic-resistant bacteria ubiquitous in hospitals, nursing homes, food processing plants, and animal breeding facilities. This has raised the need for different approaches to keep pathogenic microorganisms at bay. One such alternative is the use of copper surfaces in hygiene-sensitive areas. While this approach is not novel (7), it had lost importance and acceptance in the last few decades. A 1983 report documenting the beneficial effects of using brass and bronze on doorknobs to prevent the spread of microbes in a hospitals remained largely unnoticed (18). Similarly, the idea of using copper vessels to render water drinkable has been revived only very recently as a low-cost alternative for developing countries (37). Currently, there is an intense interest in the use of copper as a self-sanitizing material, and many recent publications deal with mechanistic aspects of “contact killing” (contact-mediated killing) by copper.

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