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

• 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; this can develop by natural selection as follows:

  • Within a bacterial population there is 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 and is known as an antibiotic resistant strain

• Bacteria can evolve rapidly because they reproduce at a fast rate

• Resistant strains of bacteria can spread easily because:

  • routine antibiotic treatment is ineffective

  • people are not immune to it

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MRSA

• An example of an antibiotic resistant strain of bacteria is MRSA

  • MRSA = methicillin resistant staphylococcus aureus

• If someone gets infected with MRSA they cannot be treated easily and the bacteria are resistant to standard antibiotic treatments

• To slow the development of antibiotic-resistant strains like MRSA:

  • 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 antibiotics

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

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