A person infected with the bacteria MM294 is instructed by a doctor to take an antibiotic for ten days. However, the individual stops taking the medication after only three days, feeling better. How does this example illustrate how a bacterial population can evolve over time?

When an individual infected with bacteria such as MM294 is prescribed antibiotics, the medicine works by killing the bacteria causing the infection. However, not all bacteria may be equally affected by the antibiotic; some might be naturally resistant to the drug due to genetic variation within the bacterial population.

In the given scenario, the person stops taking their antibiotics after three days because they feel better, even though the treatment was supposed to last for ten days. This premature cessation of antibiotic treatment can lead to an incomplete killing of the bacteria. The bacteria that survive are more likely to be those with resistance to the antibiotic, since the sensitive ones would have been killed off initially by the medicine.

Given that bacteria reproduce quickly, these resistant bacteria will then multiply, and the bacterial population in the person’s body will gradually become more composed of these antibiotic-resistant bacteria. If the individual gets sick again, the antibiotic that was initially prescribed may no longer be effective against this now-resistant bacterial population.

This is an example of natural selection, a key mechanism of evolution. The antibiotic applies a selective pressure on the bacteria, where only those with resistance can survive and reproduce. Over time, with repeated instances of incomplete treatment, this can lead to the evolution of a bacterial population that is largely resistant to a particular antibiotic or sometimes multiple antibiotics, which is a major concern in the treatment of infectious diseases.

Extra: The concept mentioned in this scenario ties into two important biological principles: genetic variation and natural selection.

Genetic variation within a population means that individuals have slight differences in their DNA, leading to different traits. Some of these traits can confer an advantage in certain environments, such as resistance to an antibiotic in bacteria.

Natural selection is the process through which individuals with traits that confer an advantage in a particular environment have a better chance of surviving and reproducing, passing those advantageous traits to their offspring. Over successive generations, these traits become more common in the population.

One aspect of bacteria that makes them particularly adept at evolving resistance is their high reproduction rate, allowing for rapid generation turnover. Additionally, bacteria can exchange genetic material through processes such as conjugation, transformation, and transduction, which can spread resistance traits between not only individuals but also different species.

The evolution of antibiotic resistance in bacteria is a real-world problem that makes treating bacterial infections more difficult. This is why doctors stress the importance of completing antibiotic treatments even after symptoms have subsided, as prematurely ending a course of antibiotics can contribute to the development and spread of resistant bacterial strains.