A level Biology B · Edexcel 9BI0 · Topic 6E
Antibiotics and antibiotic resistance
Key points
- Antibiotics kill or inhibit bacteria but do not affect viruses or human cells.
- Bactericidal antibiotics kill bacteria (e.g. by weakening the cell wall so it bursts); bacteriostatic ones stop growth (e.g. by blocking protein synthesis at 70S ribosomes).
- Test effectiveness with antibiotic discs on a bacterial lawn and measure the zone of inhibition (area = ).
- Resistance: a random mutation gives some bacteria resistance; antibiotics kill the others, so resistant bacteria survive, reproduce and pass the allele on (also by plasmid transfer).
- Examples include MRSA and C. difficile in hospitals.
- Reducing resistance: prescribe only when needed, finish the course, rotate antibiotics, use less in farming, and good hospital hygiene.
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Antibiotics are chemicals that kill bacteria or stop them growing while doing little harm to human cells. Their success has been undermined by the evolution of resistance, which is natural selection happening fast enough to measure.
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