Why resistance is inevitable
Antimicrobial resistance is not a malfunction — it is natural selection doing exactly what it does. In any large bacterial population, a few cells carry random mutations that happen to blunt a drug. Give the drug, and the susceptible cells die while the lucky survivors multiply into a resistant population. Bacteria also swap resistance genes directly with each other on small DNA loops called plasmids, so resistance can spread between species without any new mutation at all.
Four tricks bacteria use
- Destroy the drug — bacteria make enzymes that chew it up. Beta-lactamases snip the beta-lactam ring, which is why we pair some penicillins with a beta-lactamase inhibitor to protect them.
- Change the target — a small tweak to the drug's binding site means the drug no longer fits, raising the MIC. MRSA does exactly this with its penicillin-binding protein.
- Pump it out — an efflux transporter actively bails the drug back out of the cell before it can act, lowering its internal concentration.
- Lock the door — the bacterium changes its outer membrane so the drug can't get in to begin with, narrowing the effective spectrum against it.
What good prescribing does
We can't stop evolution, but we can slow it. The core habits of 'antimicrobial stewardship' all aim at one thing: expose bacteria to drugs less often and less wastefully.
- Don't use antibiotics for viral illnesses — colds and most sore throats won't respond, and the drug only breeds resistance.
- Choose the narrowest drug that works once the organism is known, and stop as soon as the course is complete.
- Support medication adherence — finishing the prescribed course as agreed reduces the chance that partially-treated survivors regrow as resistant.
- Reserve chemoprophylaxis (preventive antibiotics) for situations with proven benefit, like specific surgeries, rather than routine use.