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Human Pathogens are Unlikely to Develop “Copper-Resistance”

By Harold Michels, Antimicrobial Copper Expert & Advisor to the CDA

Many medical professionals are concerned about the emergence of antibiotic resistant bacteria, or “superbugs” such as MRSA, VRE, and more recently CRE.  These and other antibiotic-resistant organisms are a dangerous concern for hospitalized patients, who often suffer from suppressed immune systems.

According to the Centers for Disease Control and Prevention (CDC), the death rate from contracting these infections can be as high as 50 percent. In previous blogs and in seminars throughout the U.S., I’ve shared information with healthcare professionals, facility managers, manufacturers, fabricators and consumers about the value of Antimicrobial Copper surfaces and how they can help us fight infection-causing bacteria.   However, some medical professionals have raised the issue of the potential emergence of copper resistant bacteria – an unintended consequence of the deployment of copper-touch surface products in hospitals or medical facilities.   Examples of copper resistant bacteria can be found in research literature but these examples do not apply to bacteria exposed to solid copper alloy touch surfaces.

Muller Hinton agar with 4% NaCl showing a lawn culture of Staphylococcus aureus (MRSA)that is resistant to oxacillin disk (1 μg). Photo courtesy of Wikipedia

In order to best explain the difference between copper resistance (as it’s cited in the literature) and antibiotic resistance, the mode of action or kill mechanism for copper and antibiotics needs to be described.  Antibiotics are typically designed to be selective. Antibiotics work inside the human body and are designed to kill, or inhibit the growth of the targeted bacteria, but not the cells in the body. Each type of antibiotic affects the targeted bacteria in a different way. For example, a specific antibiotic might weaken a cell wall, or disrupt a metabolic reaction, resulting in the death of the targeted bacteria.

In contrast to antibiotics, copper alloy surfaces, which are intended for use outside the human body, are not selective, in that they kill both Gram negative and Gram positive bacteria.  The ability to kill the following six bacteria, when they come into contact with copper alloy surfaces, has been recognized by the US Environmental Protection Agency (EPA) after extensive testing under prescribed protocols:

  • Staphylococcus aureus 
  • Enterobacter aerogenes
  • Escherichia coli O157:H7
  • Pseudomonas aeruginosa
  • MRSA (Methicillin-Resistant Staphylococcus aureus)
  • VRE (Vancomycin-Resistant Enterococcous faecalis)

Copper Key Pad, Operator Interface Technology Inc

Even though only six bacteria are currently registered with the EPA, no bacterial, viral, or fungal specie has been found to survive on solid copper alloy surfaces.

In regard to the copper kill mechanism, the consensus is that the mode of attack is multi-targeted. Copper interacts with the cell membrane, causing it to rupture, thus leading to loss of cytoplasmic content. The copper ions then enter the cell and induce the generation of reactive oxygen species. This further compromises cell integrity, resulting in the interference with metabolism, and binding to enzymes that control other vital cell functions which leads to DNA degradation. The net result is rapid cell death in a matter of minutes.

The existing literature on “copper resistance” refers to studies of bacterial species in aqueous solutions containing copper compounds, such as copper chloride or copper sulfate. It is suggested that the copper-containing aqueous solution kill mechanism differs from that seen on copper alloy surfaces. The latter provides an almost unlimited source of high concentration copper, which is not the case in copper-containing aqueous solutions, where the copper concentration is low. The so-called “resistant bacteria” do survive in copper-containing aqueous solutions for a slightly longer period before they die. However this copper resistance is not comparable to antibiotic resistance because antibiotic-resistant bacteria are able to grow and multiply in the presence of the antibiotic. Thus “copper resistance” in copper-containing aqueous solutions might more accurately be termed “copper tolerance.”

In summary, the development of copper resistance is unlikely, because of the multi-targeted mode of attack, which results in rapid death. Copper has been used by man since the Bronze Age, which was 10,000 years ago, and no copper resistant human pathogen has been found to date. Copper alloy surfaces have been shown to significantly reduce microbial contamination. Thus, the use of copper alloy surfaces in a variety of venues, particularly hospitals, should result in a reduction in antibiotic use and suppress the emergence of antibiotic resistant strains of bacteria.

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