3.2 Evolving resistance to antibiotics

Allow about 10 minutes

Darwin’s theory was that evolution by natural selection would occur if the following conditions were met:

• There is a struggle for existence. Survival is limited by environmental constraints, so that there is competition, and not all individuals will survive to produce offspring.
• There is variation between individuals. Individuals with advantageous traits will have a greater probability of survival under these conditions and are therefore more likely to reproduce.
• The characteristics, or traits, of an individual are inherited. Advantageous traits that promote survival will be inherited by the next generation so that these traits become increasingly common in the population.

Now answer the following questions about the evolution of antibiotic resistance.

Within a bacterial population, some bacteria will be sensitive to antibiotic treatment while others will have acquired resistance to antibiotics, via either genetic mutation or horizontal gene transfer. In the presence of antibiotics, the resistant bacteria have a survival advantage over the sensitive bacteria and are more likely to survive and reproduce. Because bacteria reproduce so quickly, resistant bacteria can quickly dominate the population (Figure 10).

Of course, changes to the bacteria’s environment made by us can affect the evolution of antibiotic resistance. You will return to this theme when you look at how our use of antibiotics contributes to the rise of antibiotic resistance bacteria in Week 5.