Resistant Bacteria (AQA GCSE Biology): Revision Note

Mutations & bacterial evolution

• The theory of evolution by natural selection is now widely accepted and many sources of data are now available to support the theory of evolution

• One very clear piece of evidence for evolution is antibiotic resistance in bacteria

• An antibiotic is a chemical that can kill or inhibit the growth and reproduction of bacteria

• Antibiotics are extremely useful to humans as some bacteria are pathogenic and can cause life-threatening disease

• Bacteria reproduce, on average, every 20 minutes and therefore evolution occurs in a much shorter time span

• Like all other organisms, within a population, there will be variation caused by mutations

• A chance mutation might cause some bacteria to become resistant to an antibiotic (e.g. penicillin)

• When the population is treated with this antibiotic, the resistant bacteria do not die

• This means they can continue to reproduce with less competition from non-resistant bacteria, which are now dead

• Therefore the genes for antibiotic resistance are passed on with a much greater frequency to the next generation

• Over time the whole population of bacteria becomes antibiotic-resistant because the bacteria are best suited to their environment

Diagram of the development of antibiotic resistance

Use this image

• This is an example of natural selection that humans have helped to develop due to overuse of antibiotics in situations where they were not really necessary

• Therefore, to slow the development of antibiotic-resistant strains:

  • Doctors should avoid unnecessary prescriptions, such as for viral or mild infections

  • Patients must complete their antibiotic course to ensure all bacteria are eliminated, preventing resistant mutations

  • Antibiotic use in agriculture should be limited to reduce resistance spread

• Developing new antibiotics is expensive and slow, making it difficult to keep pace with emerging resistant strains

MRSA

• Increases in the population of antibiotic-resistant bacteria cause infections and diseases which are harder to control as it is difficult to find antibiotics that certain strains of bacteria are not resistant to

• An example of this is MRSA, a very dangerous bacterial strain that is resistant to most antibiotics

• If someone gets infected with MRSA they cannot be treated easily

Developing antibiotics

• The current increase in antibiotic resistance is encouraging drug companies to develop new antibiotics that are effective against these new resistant strains, such as MRSA

• However, the number of new antibiotics discovered has slowed significantly

• Developing new antibiotics is also a very costly process

• Some scientists are worried that the demand for new antibiotics may not be met, as more and more antibiotic-resistant strains evolve