When it Comes to Bacteria and Copper: Resistance is Futile

There is a lot of news about antibiotic resistance. Bacteria that are exposed to antibiotics and survive go on to pass that resistance to future generations, creating what we call "superbugs," bacteria that can only be killed with the most powerful antibiotics - if at all. These multi-drug resistant organisms are a growing problem in healthcare and a major cause of fatal hospital-acquired infections.

If bacteria can become resistant to powerful antibiotics, why won't they become resistant to copper? Today we will explore two major reasons.

First, a preamble. Any good scientist will tell you that no fact is 100% certain. So while we can't guaranted that no bacteria will ever somehow become resistant to copper (because science always leaves room for the inconceivable), we can share with you these two reasons that make that probability extraordinarily slim.

#1 Copper kills bacteria in five simultaneous ways.

Copper's biocidal properties focus on five mechanisms. Each of these mechanisms all by itself is lethal, multiple mechanisms at the same time is lethal more efficiently. Therefore, for a bacteria to become resistant to copper, it would have to spontaneously mutate in such a way that all five methods are rendered ineffective - at the same time. One mutation at a time is far more likely, maybe two or in an extraordinary case, three. But five simultaneous mutations that defeat all five mechanisms is just, well, inconceivable.

#2 Copper is an essential metal, without which bacteria would die.

In a wonderful catch-22 (wonderful for us, bad for bacteria), copper is both essential and lethal to bacteria. As a cofactor in certain enzymes and for its ability to oxidize, copper plays a critical part of any cell's functions, including bacteria cells. However, free copper is poisonous and physically destructive to bacteria. While bacterial cells have their own defence mechanisms against taking in too much copper, these mechanisms are not sufficient to overcome the effect of copper concentrations found in raw copper, copper alloys, and cuprous-oxide infused materials. Most importantly, for resistance against copper to develop, the very nature of cell biology would have to change. The cell would have to find some other way of reducing and oxidizing, and some other combination of atoms to form links in the enzyme molecules.

Let's explore how inconceivable this is by looking at how cells started to use copper in the first place. Around 2.3 billion years ago, Earth experienced a Great Oxygenation Event. This global environmental change led to significantly more dioxygen (O₂) in the atmosphere, and fundamentally changed the way all living things (at this point, mostly cyanobacteria) processed nutrients. This global event led to the development of copper-based oxidation mechanisms. So a global environmental change which impacts the atmosphere and bioavailablilty of elements could conceivably, over millions of years, enable some drastic evolutionary change. But the scale of this event is just too enormous to play a role. It's just... inconceivable. (Keep in mind that while this unfathomable transformation is being made, copper's other destructive mechanisms would be destroying the bacteria membrane anyway. If there are even humans and hospitals in a few million years).

So there we have it. Two very strong reasons to believe that when it comes to bacteria, resistance to copper is futile.