Resistant Bacteria (AQA GCSE Biology: Combined Science)

• 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 (eg 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

Development of antibiotic resistance in bacteria

• 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, for example:
  • For the treatment of non-serious infections
  • Routine treatment to animals in agriculture
  • Failure to finish the prescribed course of antibiotics

• 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

• The increase we are currently seeing 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 we may not be able to keep up with the demand for new antibiotics, as more and more antibiotic-resistant strains evolve