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Fighting bacteria with copper

The views expressed are those of the author and are not necessarily those of Scientific American.

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Along with the main elements of carbon, oxygen, nitrogen, magnesium and sulphur, organic organisms also require trace amounts of certain other elements, including some metals. The most useful thing about the metals required by the body is that their outer electron orbitals are very close together, making it easy for them to both accept and loose a few electrons here and there. By holding and releasing electrons they can take place in redox reactions, which are used to produce energy for the cell.

Copper can cycle between two different ionic forms: Cu+ and Cu2+. Its most important use is as an electron carrier for the process of creating the energy-rich molecule ATP. Although it is vital to the cell in small amounts, in large quantities it can become toxic. By ‘large quantities’ we are talking about greater than one atom per cell, so anyone suggesting that consuming or being close to large quantities of copper is beneficial for your health is probably wrong.

Copper mineral. Consumption not recommended. Image credit below.

Large amounts of copper are toxic for pretty much all living cells, which can be exploited by the human immune system to fight off invading bacteria. When macrophages (the white blood cells that surround and break down invading bacteria) are activated and engulf a bacteria they start to accumulate copper ions inside the cell, in particular in the part of the cell that has just engulfed the bacteria. As a response, many bacteria have increased resistance to copper ions, and those that have lost this resistance are more susceptible to being broken down by the macrophages. While large amounts of copper are indeed bad for your cells, inadequate copper levels can compromise the immune system and make people more likely to suffer from bacterial infection.

As bacterial cells are much smaller and more compact than human cells, they tend to keep all their copper-containing enzymes very close to the cell membrane, to prevent them causing unwanted redox reactions inside the cell. When presented with elevated copper levels, the bacteria can turn on a group of genes which produce proteins capable of shuttling copper out of the cell. These are the copper resistance genes. As a large number of pathogenic bacteria contain these copper-resistant genes, and as there are very few copper-containing enzymes in bacteria, it is likely that an excess rather than a deficit of copper is a problem for bacteria inside the human body.

If you do feel you need more copper in your life, these are the foods you should be eating! From the Agricultural Research Service, the research agency of the United States Department of Agriculture, credit below.

The use of copper as a strategy against bacteria may have important clinical implications. While using copper as a therapeutic strategy would be potentially dangerous for the host, targeting bacterial copper resistance may provide help for the macrophages and immune system cells to clear the bacteria naturally. Developing a way to compromise the bacteria by reducing their copper resistance could also be used along with antibiotic therapy in order to increase the effectiveness of the antibiotic.

Credit link for image 1

Credit link for image 2

Reference: Festa RA, Thiele DJ (2012) Copper at the Front Line of the Host-Pathogen Battle. PLoS Pathog 8(9): e1002887. doi:10.1371/journal.ppat.1002887

S.E. Gould About the Author: A biochemist with a love of microbiology, the Lab Rat enjoys exploring, reading about and writing about bacteria. Having finally managed to tear herself away from university, she now works for a small company in Cambridge where she turns data into manageable words and awesome graphs. Follow on Twitter @labratting.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. mem from somerville 10:29 am 10/14/2012

    Huh. What about the use of all those copper pesticides by organic farmers? Could that create a resistance problem?

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  2. 2. YangHui 10:36 pm 10/14/2012

    @mem from somerville: It probably could, yeah. As Science Sushi explains in this post: , just because something is organic doesn’t mean it’s healthy or even sustainable.

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  3. 3. S.E. Gould in reply to S.E. Gould 2:21 pm 10/15/2012

    thanks for the comments! Copper pesticides will indeed encourage copper resistance in bacteria, and the sharing of copper resistance into new species. Whether this impacts the copper-resistance of pathogenic bacteria would require some research, but it does definitely encourage copper resistance among the plant pathogens.

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  4. 4. Phathisani 3:37 pm 10/15/2012

    Some time ago I had students swab door handles in the university and plot the results. The expectation was that those nearest the toilets would be most heavily contaminated with reductions linked to distance. The crude results seemed completely random. Observation showed that the doors in this 150 year old building had either original brass handles/push plates or stainless steel replacements. The bacterial counts linked to the metal irrespective of the distance. That these brass (i.e. copper containing) surfaces were having such a dramatic effect after a century and a half suggests that any copper-resistance of pathogenic bacteria was not significant in that environment. As said, more research is necessary as, if copper is to be used (say) as an adjunct to antibiotics, then the environment in which the therapy is used may become important. Some houses now have mostly plastic plumbing whilst others have 100% copper pipework.Would this have a significant effect on the efficacy of treatments? Would high copper intakes from plumbing promote resistance?

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  5. 5. S.E. Gould in reply to S.E. Gould 3:11 am 10/16/2012

    @Phathisani: that sounds like really interesting research. The reason that bacteria would not be resistant to the copper in the door handle is because bacterial copper resistance consists of sequestering or pumping out copper ions. This works with the small amounts of copper that the macrophages produce but isn’t as effective on a doorknob covered in copper! My guess would be that copper pipework would actually be slightly antimicrobial. The concentration of copper in them is far too unnaturally high to promote resistance.

    As you say, more research would definitely be needed as high copper concentrations are toxic for humans as well as bacteria. Therapy based on this information is more likely to focus on knocking out bacterial copper resistance in order to make the immune system more effective.

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  6. 6. CuKing 12:54 pm 10/17/2012

    I wanted a clarification on the potential for bacteria to mutate a form or resistance to copper. I thought the effectiveness of copper was the ability to destroy the bacterial cell wall, hence avoiding the potentail for mutation. Is this just true for metallic vs ionic forms of copper?

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