Human Pathogens are Unlikely to Develop "Copper-Resistance"
In order to best explain the difference between copper resistance and antibiotic resistance, the mode of action, or kill mechanism 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 alloys 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:
• MRSA (Methicillin-Resistant Staphylococcus aureus)
• VRE (Vancomycin-Resistant Enterococcous faecalis)
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.
There is a body of literature on "copper resistance". However, these studies are conducted in aqueous solutions containing copper compounds, such as copper chloride and copper sulfate. It is suggested that the copper-containing aqueous solutions 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.
