With the changing public perception on touch surfaces following the outbreak of the Covid-19 virus, can copper, with its inherent anti-microbial properties, offer a solution to reduce virus transmission?
Copper is an essential nutrient and required for several metabolic functions by all living cells, including bacteria. Bacteria tightly regulate their internal copper levels and have evolved several mechanisms for doing this. However, when a bacterium is placed/lands on a copper surface, a series of events are triggered that result in these mechanisms being overwhelmed and causing excess copper to flood into the cell, leading to rapid death. This intimate interaction between bacteria and a copper surface is described as ‘contact killing’.
The mechanism—complex by nature—but the effect is simple.
Science suggests that copper inactivates bacteria with a multifaceted attack. The questions and answers below summarise active and ongoing research seeking to explain how copper is a highly effective touch surface.
How does contact with a copper surface affect bacteria?
Science suggests that copper surfaces affect bacteria in two sequential steps: the first step is a direct interaction between the surface and the bacterial outer membrane, causing the membrane to rupture. The second is related to the holes in the outer membrane, through which the cell loses vital nutrients and water, causing a general weakening of the cell.
How can copper punch holes in a bacterium?
Every cell’s outer membrane, including that of a single cell organism like a bacterium, is characterised by a stable electrical micro-current. This is often called “transmembrane potential”, and is, literally, a voltage difference between the inside and the outside of a cell. It is strongly suspected that when a bacterium comes in contact with a copper surface, a short circuiting of the current in the cell membrane can occur. This weakens the membrane and creates holes.
Another way to make a hole in a membrane is by localised oxidation or “rusting”. This happens when a single copper molecule, or copper ion, is released from the copper surface and hits a building block of the cell membrane (either a protein or a fatty acid). If the “hit” occurs in the presence of oxygen, we speak of “oxidative damage”, or “rust”. An analogy is rust weakening and making holes in a piece of metal.
After punching holes, how do copper ions further damage the cell?
Now that the cells main defence (its outer envelope) has been breached, there is an unopposed stream of copper ions entering the cell. This puts several vital processes inside the cell in danger. Excess copper literally overwhelms the inside of the cell and obstructs cell metabolism (i.e. the biochemical reactions needed for life). These reactions are accomplished and catalysed by enzymes. When excess copper binds to these enzymes, their activity grinds to a halt. The bacterium can no longer “breathe”, “eat”, “digest” or “create energy”.
How can copper’s effect be so fast, and affect such a wide range of microorganisms?
Experts explain the speed with which bacteria perish on copper surfaces by the multi-targeted nature of copper’s effects. After membrane perforation, excess copper can inhibit any given enzyme that “stands in its way”, and stop the cell from transporting or digesting nutrients, from repairing its damaged membrane, from breathing or multiplying.
It is also thought that this is why such a wide range of microorganisms are susceptible to contact by copper. This includes viruses, which cannot complete their life cycle without exploiting a suitable host cell. They use the host cell’s metabolic systems for producing more viruses which can then infect more cells. Copper alloys can permanently and irreversibly inactivate viruses, most likely by disrupting their ability to invade host cells.