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Humans vs. bacteria

Even as weapons labs turn out new weaponry, other labs turn out defensive counter-measures; to which the weaponeers respond with counter-counter-measures. Ad infinitum … arms races never end.

Nor are arms races new. Looking back half-a-billion years, the fossil record reveals creatures evolving mouths and teeth … shells to ward off those teeth … sharper teeth … thicker shells … mouth parts to drill through thick shells ….

For three-plus billion years before the evolution of mouths and teeth, single-celled organisms attacked their neighbors and defended themselves with poisons.



The key to bio-chemical warfare is selective toxicity – producing chemicals that poison your adversary, but not you or your friends.

Humanity discovered such microbial toxins – antibiotics – nearly a century ago. Antibiotics were so effective, some scientists believed they could vanquish disease.




Such optimism failed to account for bacterial versatility … and the bacterial world’s three-plus billion-year head-start.

No sooner had doctors begun using antibiotics in the 1940s than antibiotic-resistant bacteria infected their patients.

Antibiotic resistance no doubt evolved billions of years ago, shortly after the evolution of antibiotics. But such resistance carries a price: it costs energy, and slows down growth, a disadvantage that, in an antibiotic-free environment gives a bacterium’s non-resistant cousins an edge in the competition for food and space.

Inject an antibiotic into the environment, however, and the non-resistant bugs die off, leaving the slow-growing but resistant strains to thrive. Antibiotics drive evolution, selecting for the resistant minority.

A high school student mounting a science fair project, wishing to study the evolution of drug resistance, might begin by exposing bacteria to an unrelenting barrage of drugs … a common practice of industrial agriculture … or mix antimicrobial chemicals into common consumer products, for instance, dish detergents and hand soap (despite evidence that antibacterial cleansers confer no advantage to the consumer, but do pollute our waterways, challenging myriad bugs to develop resistance).

Different bacteria resist antibiotics in different ways: some, by pumping antibiotic molecules out of their single-celled bodies; others, by barring entry of the molecules in the first place; some can alter their metabolism so the antibiotic is no longer toxic; and some destroy the antibiotic molecule outright.

The “blueprints” for resistance are carried on genes. Bacteria inherit their genes as we do: vertically, from parent to offspring. But …

… Bacteria can also inherit genes horizontally, passing genetic material from one to another. A bug resistant to one antibiotic can pick up resistance to other antibiotics from its neighbors.

Antibiotic-resistant is not new. What is new are “bugs” that are simultaneously resistant to many different antibiotics.

Until World War II, most battle-related deaths resulted, not from wounds directly, but from the infections that followed. Until antibiotics, infection was often a death sentence.

It would be unfortunate if, through unwise use, antibiotics and antimicrobials were to become ineffective, forcing humanity to retreat to a time when infection all-too-often meant death.

Al Stahler teaches private and public science classes to students of all ages, and talks about science on KVMR radio (89.5 FM). He can be reached at stahler@kvmr.org


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