Worked example 1
A patient is prescribed a course of antibiotics for a bacterial infection. They stop taking the antibiotics once they feel better, before completing the full course. Explain how this action, over time, can contribute to the development of antibiotic resistance within the general population.
Show solution outline
- Initial Infection & Treatment: The patient's bacterial infection initially contains a large population of susceptible bacteria and a very small number of naturally resistant bacteria (present due to random mutation).
- Partial Course Effects: Taking the first few doses of antibiotics kills off the most susceptible bacteria, leading to a reduction in symptoms. However, more resilient bacteria, including the resistant mutants, survive.
- Selective Pressure and Regrowth: By stopping the course early, the remaining, more tolerant bacteria are left to multiply without competition from the susceptible strains. The antibiotic concentration drops, removing the selective pressure that was keeping them in check.
- Reproduction of Resistant Strains: These resistant bacteria reproduce, creating a new population within the patient that has a much higher proportion of resistant individuals. The patient may become ill again or become an asymptomatic carrier of a resistant strain.
- Spread of Resistance: The patient can then pass these resistant bacteria to others. If this behaviour is widespread, the frequency of resistant strains in the general population increases, making future infections in other people much harder to treat with that antibiotic.