Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!


Antibiotics and drug testing

Antibiotic resistance

Over time, bacteria [bacteria: Single-celled microorganisms, some of which are pathogenic in humans, animals and plants. Singular is bacterium. ] can become resistant to certain antibiotics [antibiotics: Substances that kill bacteria. ]. This is an example of natural selection. In a large population of bacteria, there may be some that are not affected by the antibiotic. These survive and reproduce, creating more bacteria that are not affected by the antibiotic.


MRSA is methicillin-resistant Staphylococcus aureus. It is very dangerous because it is resistant to most antibiotics. To slow down or stop the development of other strains of resistant bacteria, we should:

  • always avoid the unnecessary use of antibiotics
  • always complete the full course



You may wish to view this BBC News item from 2007 about how drug-resistant strains of TB are putting European Union states at risk of a deadly outbreak.

Tuberculosis, or TB for short, is a disease caused by a bacterium called Mycobacterium tuberculosis. Most people who are infected do not show any symptoms. But about 10 per cent go on to develop serious symptoms including shortness of breath, coughing, fever, and even death.

Infected people without symptoms are usually given a course of one antibiotic [antibiotics: Substances that kill bacteria. ]. Those who show symptoms need a course of several antibiotics at once. This is to reduce the chance of strains of antibiotic-resistant bacteria emerging.

Development of resistance - higher only

The main steps in the development of resistance are:

  1. Random changes or mutations occur in the genes of individual bacterial cells.
  2. Some mutations protect the bacterial cell from the effects of the antibiotic.
  3. Bacteria without the mutation die or cannot reproduce with the antibiotic present.
  4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains.

Back to Keeping healthy index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.