Explain how antibiotic resistance in bacteria can be an example of rapid evolution. Discuss the roles of selective pressure, mutation, and horizontal gene transfer, using the example of the $\beta$‑lactamase gene in ‘Escherichia coli’ conferring resistance to ampicillin.

Step-by-step solution

1. 1. Define rapid evolution: evolutionary change occurring over a few generations, often observable in laboratory or clinical settings.
2. 2. Identify selective pressure: introduction of the antibiotic ampicillin creates a strong selection for bacteria that can survive its killing effect.
3. 3. Describe mutation: spontaneous point mutations in the chromosomal DNA or plasmid DNA can create or activate a $\beta$‑lactamase gene, enabling the bacterium to hydrolyse the amide bond of ampicillin.
4. 4. Explain horizontal gene transfer (HGT): plasmids carrying the $\beta$‑lactamase gene can be transferred between bacteria by conjugation, transformation or transduction, spreading the resistance trait rapidly across populations.
5. 5. Integrate the example: ‘E. coli’ that acquires a plasmid with a functional $\beta$‑lactamase gene becomes resistant; under ampicillin pressure, these bacteria thrive and reproduce, while susceptible ones die off. The resistant genotype increases in frequency within a few generations, demonstrating rapid evolution.
6. 6. Conclude that the combined effect of selective pressure (ampicillin), mutation (creation/activation of the gene), and HGT (plasmid spread) leads to a swift increase in antibiotic resistance, illustrating evolution in action.

Concept tested: Evolutionary mechanisms

Published 28 September 2026 · How this solution was prepared and checked