Why Copper?

I read a compelling headline in yesterday’s Wall Street Journal:  Paging Dr. Copper: Metal Wins Fans in Health Care

It actually wasn’t so much the headline that grabbed my attention, but the caption in the accompanying infographic:

Beating Bacteria: Research shows bacterial colonies are generally more prevalent on non-copper substances.

Fascinating!  The infographic goes on to state that non-copper hospital bedrails contain 6,471 bacterial colonies per 100 square centimeters, versus 366 on copper hospital bedrails.  In fact, the results were compelling for every surface (IV Pole, Chair, Tray Table, Call Button) except for “data-input device” (cue image of a computer keyboard), in which case the copper surface contained 50% more bacterial colonies.  Ouch!  And puzzling.

A later infographic states that copper kills bacteria by “drawing electrons out of the cell and pumping copper ions in.”  OK. It further states that “the cell’s membranes collapses, it loses nutrients and water, and its DNA and proteins are destroyed.”

Bacteria killed by copper include E coli, MRSA, and staph.  This is very cool!  And I’m impressed by the infographics.

Now, some questions.

1) (less important) Which hospitals have copper bedrails? And copper computer keyboards?? Granted, luckily I don’t spent a lot of time in hospitals but it sounds so fancy!

2) (more important) Why copper?  What is it about copper, and not other metals, that drains bacteria of their electrons?  Is it copper’s electronic structure?  Is it the arrangement of atoms in the element?  Is it something about the copper surface?

3) (Not so much a question, but a musing)  Why don’t articles explain more of the details more often?  I don’t need a journal article in the WSJ, but I would have liked to see a brief mention of the other metals I learned about below, the oligodynamic effect (see below), and a statement on what we know, today, in 2016 about this and what we don’t know.  I am troubled at how science articles for the masses generally tend to be devoid of details, and thus it’s very hard to understand on a molecular or atomic level what is going on (see Friday’s upcoming post on CRISPR in National Geographic).  And I think your average Joe or Josephine can handle it!

So, I’m now on a quest to address question 2.  Then we can return to the computer keyboard outlier question, but I welcome your theories in the comments!

Some early learnings:

A) A quick wikipedia search reveals that copper and its alloys (brass, bronze, etc) kill bacteria.  OK, so it’s not just pure copper.

B) Both the WSJ article and the wikipedia entry cite knowledge in the ancient world of the antimicrobial properties of copper.  Apparently, centuries ago people observed that water transported in copper vessels contained less slime than water in vessels made of other materials.

C) The wikipedia article states that the how of all of this is still unknown and under active investigation.  Interesting!  I love when science is mystifying.  The article offers a summary of some recent advances, theories, and questions:

  1. the oligodynamic effect (discovered in 1893 by the Swiss botanist Carl Naegeli): the idea here is that the metal reacts with the thiol (sulfur and hydrogen) and amine (nitrogen and hydrogen) parts of proteins.  Thiol and amine groups are pretty ubiquitous, so no surprise that a reaction with them will have an adverse effect on bacterial life.
  2. Copper is NOT THE ONLY metal exhibiting this effect!  Other bacterial enemies: mercury, silver, iron, lead, aluminum, zinc, bismuth, and gold.  OK, that’s a lot of metals (what’s up with the omission WSJ?).  Importantly, the WSJ did mention that stainless steel does not exhibit antimicrobial properties.  What is stainless steel made of? generally, iron, carbon, and chromium.  Huh.  So apparently the presence of carbon and chromium, or the proportion of carbon and chromium prevent iron from doing its oligodynamic work.  Or, perhaps iron just isn’t as good at the job.

This would be a good time to consult the Periodic Table.  In general, elements near each other on the Periodic Table, and especially in the same column (also known as Family) tend to exhibit similar behavior.  Let’s check out the locations of these oligodynam-ators!

 

WhyCopper.001   (I’m terribly pleased with myself for making and inserting my first graphic into a blog post.  This periodic table came from sciencenotes.org and I added the red circles in Keynote.)

So what are we looking at?  The metals generally seem to cluster near each other, with iron and bismuth somewhat far away, and aluminum a bit of an outlier too.  Could this explain stainless steel’s failure as an antimicrobial?

I’m going to have to stop here as my coffee shop office is closing! Look for Part 2 either later today or at some point soon over the next few days.

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