Outline how bacteria become resistant to antibiotics as an example of natural selection

Sourav PanNovember 1, 2024

Answered

Bacteria can become resistant to antibiotics through a process that exemplifies natural selection. This phenomenon occurs through several mechanisms, including mutations, horizontal gene transfer, and the selective pressures imposed by antibiotic use. Here’s an outline of how these factors contribute to the development of antibiotic resistance in bacterial populations.

Mechanisms of Antibiotic Resistance

1. Mutations

Bacteria reproduce rapidly, often doubling in number every 20 minutes under optimal conditions. During this process, errors can occur when DNA is copied, leading to mutations. Some of these mutations may confer resistance to antibiotics:

• Random Mutations: Spontaneous genetic changes can result in traits that allow bacteria to survive exposure to antibiotics. For example, a mutation might alter the target site of an antibiotic, rendering it ineffective.
• Selective Advantage: When an antibiotic is introduced into an environment, bacteria without resistance are killed off while resistant variants survive and reproduce. This selective pressure increases the frequency of resistant alleles in the population over time

2. Horizontal Gene Transfer

Bacteria can acquire resistance genes from other bacteria through horizontal gene transfer (HGT), which includes mechanisms such as transformation, transduction, and conjugation:

• Transformation: Bacteria can take up free DNA from their environment, which may contain resistance genes.
• Transduction: Bacteriophages (viruses that infect bacteria) can transfer DNA between bacterial cells.
• Conjugation: Direct transfer of DNA between bacteria through physical contact allows for rapid dissemination of resistance traits.

This ability to share genetic material accelerates the spread of antibiotic resistance within and between bacterial populations

Natural Selection in Action

3. Selection Pressure from Antibiotics

The use of antibiotics creates a strong selection pressure on bacterial populations:

• Survival of the Fittest: When antibiotics are administered, susceptible bacteria are eliminated while those with resistance traits survive. These survivors reproduce, leading to a population dominated by resistant strains.
• Environmental Impact: Resistance can develop not only in clinical settings but also in agricultural environments where antibiotics are used for livestock. This widespread use contributes to the selection of resistant strains across various ecosystems

4. Bottleneck Effect

The bottleneck effect can also play a role in developing antibiotic resistance:

• Population Reduction: When a large population is exposed to an antibiotic, only a few resistant individuals may survive. This drastic reduction can lead to a loss of genetic diversity but also allows for rapid proliferation of the surviving resistant strains.
• Genetic Drift: The few survivors may carry specific resistance genes that become fixed in the population due to chance events following the bottleneck

References

1. ReAct – Action on Antibiotic Resistance. (n.d.). Mutations and selection. Retrieved from https://www.reactgroup.org/toolbox/understand/antibiotic-resistance/mutation-and-selection/
2. Vogwill, T., et al. (2021). The roles of history, chance, and natural selection in the evolution of antibiotic resistance. eLife, 10, e70676. https://doi.org/10.7554/eLife.70676
3. The Lancet. (2008). Antibiotic resistance: adaptive evolution. The Lancet, 371(9628), 1016-1018.
4. Nature Reviews Microbiology. (2021). Antibiotic resistance in the environment. Nature Reviews Microbiology, 19(7), 405-420. https://doi.org/10.1038/s41579-021-00649-x
5. The National Center for Biotechnology Information (NCBI). (2021). The roles of history, chance, and natural selection in the evolution of antibiotic resistance. PMC8412936. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC8412936/