The Resistance Movement: Bacteria Want to Live Too

Team BT 1The vast majority of bacteria, as it turns out, are our little buddies: They help us digest food, for example milk sugars and fiber; and they help assemble nutrients, such as amino acids, the building blocks of proteins, and vitamin K, which we need to clot blood. The surprising part, however, is they actually help us fight disease, says NYU infectious disease expert, Martin Blaser, MD, in his book, Missing Microbes: How the Overuse of Antibiotics is Fueling Our Modern Plagues. They do this, for example, by sending chemical signals to our immune system to keep it on high alert; they help to metabolize needed pharmaceuticals such as the heart drug digoxin; and they even secrete substances, including their own antibiotics, which are poisonous to foreign invaders. But they can’t do this work single-handedly; instead, bacteria have to work together in huge numbers to get the job done. For example, just one milliliter of our colon — where bacteria metabolize fiber — contains more bacteria than there are people on Earth, says Martin Blaser.

And in return for all the help they give us, how do we treat these guys? Apparently, we’re slaughtering them in droves with our indiscriminate use of antibiotics. Margaret Riley, PhD, and professor of biology at the University of Massachusetts, Amherst, analogizes the taking of antibiotics to the ingestion of a hydrogen bomb on the basis that it kills all of our body’s bacteria, not just the kind that’s causing a problem.

The extent of this antibiotic “bombing” is massive: Health care providers prescribed 258.0 million courses of antibiotics in 2010, or 833 prescriptions per 1000 persons. And according to the US Centers for Disease Control, 30-50% of antibiotics prescribed in hospitals are unnecessary or inappropriate. But there’s a bigger issue: 70 – 80% of all antibiotics sold in the US are used for the single purpose of fattening up industrial farm animals. In 2011, animal producers bought nearly 30 million pounds of antibiotics for the purpose of fattening up their livestock, a practice banned in Europe.

One has survival advantage: Light- and dark- colored moths against a dark background

One has survival advantage: Light- and dark- colored moths against a dark background

So when we drop over 15 tons of antibiotics a year on our bacterial population — in the US alone — we can expect a response. And just like any other living organism being bombed, bacteria don’t want to die either, and so they fight back by developing resistance to the antibiotic bombs. This development of resistance is simply evolution at work, meaning that developing resistance is inevitable. Evolution, however, much like bacteria, is often misunderstood, so it’s worth taking a closer look at it because it shows us how we’re not going to win a “war” against disease if our strategy is based on fighting nature. So here’s the classic example of evolution in action, which is defined as the change in a characteristic (color, in our example), of a population (moths), over time, i.e. generations, in response to an environmental event (the Industrial Revolution and soot production). OK, it involves the Industrial Revolution, but nonetheless it’s a rather cool example:

Nineteenth century England spawned heavy industry and with it came chimney smoke: dark sooty pollution that covered trees and buildings. Which just happened to be where the peppered moth like to hang out. There are 2 kinds of peppered moths, one is dark-colored, the other light-colored. At the time of the IR most were light-colored. But, as the bark of trees and the sides of buildings took on black soot, the light-colored moths began to stand out thus becoming more noticeable to birds, their natural predator. As a result, their population declined and the dark-colored moth population rose, as they were now camouflaged by the darkened trees.

This is evolution by means of natural selection: the environment changes, and that change ‘selects’ for some fraction of the population — dark-colored moths, in this case — and giving that population a survival advantage and thus a reproductive advantage.

Back to our bacteria. The analogue to the IR and soot is the antibiotic. The analogue to the light-colored moth that the changed environment selected against is all our bacteria that aren’t resistant to antibiotics: i.e. the vast majority that help us live healthier lives or are at least harmless. And the analogue to the dark-colored moth that the changed environment selected for, thus giving it a survival and reproductive advantage, is the bacteria that are resistant to antibiotics.

Bacteria GT3

There is one important difference with (resistant) bacteria. They have a trick up their sleeve: the ability to transfer their genes that confer resistance to antibiotics, to other (susceptible) bacteria, in real time — nicely illustrated in the above cartoon. Think of genes, Dr. Blaser says, as a deck of cards, and the transfer of genes as swapping out of one of the cards. It would be as if the dark-colored moth could hand their genes that code for their dark color to the light-colored moth sitting sitting beside it on the tree.

The upshot of our “drug abuse” — the overuse and misuse of antibiotics on our resident bacteria — is the proliferation of bacteria that are resistant to those very same antibiotics. So much so that the US Centers for Disease Control reported that:

Antibiotic resistance is a worldwide problem. New forms of antibiotic resistance can cross international boundaries and spread between continents with ease. Many forms of resistance spread with remarkable speed. World health leaders have described antibiotic resistant microorganisms as “nightmare bacteria” that “pose a catastrophic threat” to people in every country in the world.

The same CDC report said that MRSA poses a serious public health threat. The agency conservatively estimated that it caused 80,461 invasive infections and 11,285 related deaths in 2011, the last year for which statistics were available. The report also said that a much higher number of less severe infections occurred in both the community and in healthcare settings.

So here’s a question. We have two examples of evolution where organisms successfully adapted to environmental pressures: dark-colored moths and bacteria that are resistant to drugs — in each case conferring a survival advantage. But what about humans: can we think of a case where we have evolved, say over the last 50 to 100 years, in a way that has conferred a survival advantage? If so, what is our newly acquired trait that’s analogous to the dark-color in the moths or the drug-resistance in the bacteria, that gives us that advantage?

Put another way, if we can’t specify such a trait, does that mean humans have stopped evolving?

 

 

 

 

 

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