Antibiotics & Disease (WJEC GCSE Biology)

• An antibiotic is a chemical drug that can kill or inhibit the growth and reproduction of bacteria
• They are made naturally by certain fungi or bacteria and work by targeting the processes of bacterial cells, either by disrupting their structure or function or by preventing them from reproducing.
  • Penicillin was the first antibiotic, discovered in 1928 by Alexander Fleming
  • He noticed that some bacteria he had left in a Petri dish had been killed by the naturally occurring Penicillium fungal mould
  • The penicillium mould produces a chemical to prevent it from being infected by certain types of bacteria
• Different antibiotics are effective against different types of bacteria but not against viruses
• Antibiotics target processes and structures that are specific to bacterial cells; as such they do not generally harm animal cells
• Naturally synthesised antibiotics can be produced on a large scale in industrial fermenters
• These antibiotics are often then modified to make them more effective - these are semi-synthetic antibiotic
• Scientists are also able to make entirely synthetic antibiotics in a lab environment

How antibiotics work diagram

How antibiotics work on bacterial cells

Antibiotic resistance

• Bacteria reproduce, on average, every 20 minutes and therefore evolution occurs in a much shorter time period
• The process of natural selection in bacterial populations can be summarised as follows:
  • Like all other organisms, within a population, there will be variation caused by mutation
  • 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

Evolution of antibiotic resistance diagram

Development of antibiotic resistance in bacteria

Overuse of antibiotics leads to antibiotic resistance

• Antibiotic resistance is an example of natural selection that humans have helped to develop due to the overuse of antibiotics in situations where they were not necessary, for example:
  • For treatment of non-serious infections
  • Routine treatment of animals in agriculture
  • Failure to finish the prescribed course of antibiotics

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
• MRSA is most prevalent in hospital environments where the risks are higher due to patients already being in poor health
• Resistant strains are of concern, particularly as the number of new antibiotics being discovered has slowed significantly

Controlling MRSA

• Strict control measures in hospitals are important to minimise infection of patients with resistant strains, such as MRSE and also to prevent the development of new resistant strains
• MRSA control measures could include:
  • Thorough hand washing, particularly in between visits to different patients
  • Thorough cleaning of hospital wards
  • Frequent use of alcohol gels
  • MRSA screening of patients and staff