Why antibiotics stop working: antimicrobial resistance explained

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Antibiotics transformed medicine. Infections that once killed, and operations that once carried a high risk of infection, became routine. But bacteria evolve, and many antibiotics are becoming less reliable. This guide explains how resistance arises and what everyone can do to slow it. It is general information, not medical advice: always follow the guidance of your doctor or pharmacist.

Antibiotics, antimicrobials and the difference that matters

Antibiotics treat infections caused by bacteria.
Antimicrobials is the wider term, covering medicines against bacteria, viruses, fungi and parasites.
Antibiotics do not work on viruses. Colds, flu, most coughs and most sore throats are caused by viruses, so an antibiotic will not help them and can cause side effects. The NHS advises that many common infections get better on their own.

How resistance develops

Bacteria multiply quickly, and each time they divide there is a small chance of a random genetic change. Occasionally a change helps a bacterium survive an antibiotic, for example by:

Breaking down the drug with an enzyme before it can act.
Pumping the drug out of the cell.
Changing the target the antibiotic normally attacks, so the drug no longer fits.
Blocking entry by altering the cell's outer wall.

When an antibiotic is used, it kills the susceptible bacteria and leaves the resistant ones behind, with less competition. They then multiply. This is natural selection happening in real time. Bacteria can also share resistance genes directly with each other, even across different species, on small loops of DNA. That is one reason resistance can spread surprisingly fast.

Why overuse speeds it up

Every course of antibiotics puts selective pressure on bacteria, not only the ones causing the infection but also the many harmless bacteria living in the gut and on the skin. The more often antibiotics are used, especially when they are not needed, the more opportunities resistant strains have to take over. Use in farming and poor sanitation that lets infections spread also contribute.

How serious is it?

The World Health Organization lists antimicrobial resistance as one of the top global public health threats. A major study published in The Lancet, cited by the WHO, estimated that bacterial resistance was directly responsible for 1.27 million deaths worldwide in 2019 and contributed to 4.95 million. Resistant infections are harder to treat, often need stronger drugs with more side effects, and keep people in hospital longer. Many modern treatments, such as chemotherapy, organ transplants and caesarean sections, depend on antibiotics working.

What you can do

Do not ask for antibiotics for a cold or flu. If your doctor or pharmacist says you do not need them, it is because they will not help.
Take antibiotics exactly as prescribed, at the dose and for the length of time your prescriber or pharmacist tells you. If you have questions about stopping, ask them rather than deciding yourself.
Never share antibiotics or take ones prescribed for someone else or for a previous illness.
Do not keep leftovers. Take unused medicine back to a pharmacy for safe disposal rather than throwing it in the bin or down the drain.
Prevent infections in the first place: wash your hands, keep vaccinations up to date and prepare food hygienically.
Ask your pharmacist about treating minor symptoms. In the UK, pharmacists can advise on many common conditions.

What health systems and scientists are doing

Antibiotic stewardship programmes in hospitals and surgeries check that the right drug is used at the right dose, only when needed.
Surveillance networks track resistance patterns so doctors know which drugs are likely to work locally.
Research into new treatments continues, including new antibiotics, vaccines that prevent bacterial infections, and alternatives such as bacteriophages, viruses that infect bacteria. Developing new antibiotics is slow and commercially difficult, which is why protecting the ones we have matters.
Rapid diagnostic tests help doctors tell bacterial from viral infections faster.

When to seek help

If symptoms are severe, getting worse or not improving as expected, contact your doctor, a pharmacist or your local urgent care service. Signs of a serious infection, such as confusion, difficulty breathing or a rapidly spreading rash, need urgent medical attention. Do you have questions about antibiotics or resistance? Ask in the comments, and remember to check anything personal with a doctor or pharmacist.