Why Antibiotics Stop Working

Every antibiotic works the same way in one sense. It attacks something a bacterium has and you do not.

Bacteria are cells, and so are you. The list of things that only they have is short. That is why there are so few antibiotics and why they are so hard to invent.

How the main types work

Penicillin

Bacteria have a wall outside their membrane, and they rebuild it constantly. Penicillin jams the tool that builds it. The bacterium keeps growing, the wall does not keep up, and it bursts.

So penicillin only works on bacteria that are growing. It was discovered because somebody left a dish out and went on holiday.

Cephalosporins

They do the same job with a different shape. Bacteria defend themselves with an enzyme that cuts penicillin apart. Change the shape enough and the scissors no longer fit.

That shows you what the field really is. It is a race to stay one shape ahead.

Macrolides

They attack the machine that builds bacterial proteins. Your cells use a machine of a different size, and that difference is the safety margin.

Your gut bacteria have the bacterial version, which is why these drugs can upset the stomach.

Tetracyclines

They block the delivery of building blocks to the protein factory. They also bind to calcium, which is why they can stain developing teeth.

Quinolones

They attack the tool that untangles bacterial DNA so that it can be copied. They are powerful and broad, and they were prescribed too freely for a long time. They carry tendon and nerve side effects.

The reserve

A few antibiotics are kept back and almost never used, because they are the last ones that still work. Some were abandoned decades ago as too toxic and have been brought back.

You do not become resistant

Almost everybody has this slightly wrong. You cannot become resistant to antibiotics. The bacteria do.

In any population, a few bacteria are slightly different by chance. The antibiotic kills most. Those few survive and multiply into the space the others left.

You did not train them. You cleared the field for the ones that were already immune.

Bacteria share resistance

Bacteria can hand resistance to each other as a small package of DNA. They pass it to neighbours, including different species.

A harmless bacterium in your gut can pick up resistance and pass it to a dangerous one. So antibiotic use anywhere adds to resistance everywhere, and a great deal of that use is in farming.

Why there are so few new ones

The pipeline has been nearly empty for about 30 years. The science did not stop. The economics do not work.

A drug that you take for a week, and that doctors are asked to use as little as possible, does not repay what it costs to develop. Companies left the field.

What helps

The fixes are the boring ones.

• Do not take antibiotics for viruses. They do nothing for them.
• Follow your prescriber's instructions on how long to take them, not the internet's.
• Accept that most sore throats get better on their own.
• Wash your hands and get vaccinated. Infections that never happen need no antibiotics.

The short answer

Every antibiotic is aimed at one difference between bacterial cells and ours. Every use clears the field for whatever was already immune, and bacteria trade that immunity faster than new drugs can be invented.

If you have an unfinished packet at home, or you are wondering whether to start one, that question belongs to whoever prescribed it.