AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Resistant bacteria: Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce, so the population of the resistant strain rises. The resistant strain will then spread because people are not immune to it and there is no effective treatment.
Mutations in bacterial pathogens create new strains with different characteristics.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Mutations in bacterial pathogens create new strains with different characteristics. If a mutation gives resistance to an antibiotic, that strain is not killed by the antibiotic. The resistant bacteria survive, reproduce by binary fission, and pass the resistance allele to their offspring, so the proportion of resistant bacteria in the population rises. This is natural selection. The resistant strain then spreads between people because humans are not immune to the new resistant strain, and because the antibiotic no longer treats the infection effectively. For example, MRSA is a strain of Staphylococcus aureus resistant to methicillin and other antibiotics, so infections are harder to treat. Overuse of antibiotics increases selection pressure and speeds up the spread of resistance.
What earns the marks
- Mutations in bacterial pathogens produce new strains with different inherited characteristics.
- Some mutations give resistance to an antibiotic, so the antibiotic does not kill those bacteria.
- Resistant bacteria survive and reproduce by binary fission, passing the resistance allele to their offspring.
- The population of the resistant strain rises because resistant bacteria have a selective advantage when the antibiotic is present.
- The resistant strain spreads between people because people are not immune to the new strain and there is no effective antibiotic treatment.
- Antibiotic resistance is an example of natural selection in action.
- Overuse or inappropriate use of antibiotics increases selection pressure and can accelerate the spread of resistant strains.
Common mistakes and how to put them right
Saying the antibiotic causes the mutation that makes bacteria resistant.
Put it right: Mutations occur randomly; the antibiotic selects bacteria that already have a resistance mutation.
Stating that people become immune to the resistant bacterium.
Put it right: People are not immune to the new strain; the problem is that the antibiotic no longer kills it.
Describing resistance as the bacterium 'getting used to' the antibiotic.
Put it right: Resistance is an inherited characteristic produced by mutation, not a learned response.
Confusing antibiotic resistance with immunity or vaccination.
Put it right: Antibiotics treat bacterial infections; vaccination produces immunity to specific pathogens (both viral and bacterial) and does not treat an existing antibiotic-resistant infection.
Exam tips
- Use the selection sequence: mutation, variation, survival, reproduction, increased frequency.
- State clearly that the antibiotic kills non-resistant bacteria but not resistant ones, so resistant bacteria have an advantage.
- When explaining spread, mention that there is no effective treatment and that people are not immune to the new resistant strain.
- Avoid saying bacteria 'become' resistant during treatment; say resistant mutants are selected.
Try the lesson
The start of the Resistant bacteria: Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed. They survive and reproduce, so the population of the resistant strain rises. The resistant strain will then spread because people are not immune to it and there is no effective treatment. lesson, made from checked teaching notes for this specification point.
Have a go first
What produces new strains of bacterial pathogens?
Listen
Mutations in bacterial pathogens create new strains with different characteristics. If a mutation gives resistance to an antibiotic, that strain is not killed by the antibiotic. The resistant bacteria survive, reproduce by binary fission, and pass the resistance allele to their offspring, so the proportion of resistant bacteria in the population rises. This is natural selection. The resistant strain then spreads between people because humans are not immune to the new resistant strain, and because the antibiotic no longer treats the infection effectively. For example, MRSA is a strain of Staphylococcus aureus resistant to methicillin and other antibiotics, so infections are harder to treat. Overuse of antibiotics increases selection pressure and speeds up the spread of resistance. A strong answer earns marks for these points. Mutations in bacterial pathogens produce new strains with different inherited characteristics. Some mutations give resistance to an antibiotic, so the antibiotic does not kill those bacteria. Resistant bacteria survive and reproduce by binary fission, passing the resistance allele to their offspring. The population of the resistant strain rises because resistant bacteria have a selective advantage when the antibiotic is present. A common slip: saying the antibiotic causes the mutation that makes bacteria resistant. Instead, mutations occur randomly; the antibiotic selects bacteria that already have a resistance mutation. Exam tip: Use the selection sequence: mutation, variation, survival, reproduction, increased frequency.
Key words
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Antibiotic resistance
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Natural selection and selective advantage
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Mutation and new strains
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Public health and treatment failure
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See every definition
- Antibiotic resistance
- Mutations of bacterial pathogens produce new strains, and some strains might be resistant to antibiotics, so they are not killed.
- Natural selection and selective advantage
- Resistant bacteria survive and reproduce, so the population of the resistant strain rises, and this is natural selection.
- Mutation and new strains
- Mutations of bacterial pathogens produce new strains with different inherited characteristics.
- Public health and treatment failure
- The resistant strain spreads because people are not immune to it and there is no effective treatment.
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