# A new strain of tuberculosis (TB) bacteria has emerged that is resistant to several antibiotics. Explain how this resistant strain developed and why completing a full course of antibiotics is important in preventing the spread of resistant strains.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.4 Antibiotics and resistance · Explain · 5 marks

> Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis. Treatment requires patients to take a combination of antibiotics for at least six months. In some countries, patients stop taking their antibiotics once they feel better, after only a few weeks.

## Mark scheme (5 marks)

1. Some bacteria in the original population have a random mutation that gives resistance to an antibiotic
2. Antibiotic kills non-resistant bacteria / susceptible bacteria are killed, leaving resistant bacteria to survive
3. Resistant bacteria reproduce and pass on the resistance gene / allele to offspring
4. If a patient stops the antibiotic course early, some non-resistant bacteria may survive and could mutate / resistant bacteria are not fully eliminated
5. Completing the full course ensures all bacteria are killed, reducing the chance of resistant strains developing and spreading to others

## Key terms

- [antibiotic](https://www.gradenine.co.uk/glossary/antibiotic)
- [resistant strain](https://www.gradenine.co.uk/glossary/resistant-strain)

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-new-strain-of-tuberculosis-tb-fa79e04b) · Published by Druglandscape Ltd.