Describe the development of strains of antibiotic-resistant bacteria, including MRSA, as an example of natural selection

Sourav PanNovember 4, 2024

Answered

The development of strains of antibiotic-resistant bacteria, including Methicillin-resistant Staphylococcus aureus (MRSA), is a prime example of natural selection in action. This process illustrates how bacteria evolve over time in response to selective pressures, particularly the use of antibiotics. Here’s how this occurs:

1. Variation Within Bacterial Populations

• Genetic Diversity: Within any population of bacteria, there exists genetic variation due to mutations and horizontal gene transfer. Some bacteria may naturally possess mutations that confer resistance to certain antibiotics, while others may acquire resistance genes from other bacteria through processes such as conjugation or transformation.

2. Production of Many Offspring

• Rapid Reproduction: Bacteria reproduce quickly, often doubling in number every 20 minutes under optimal conditions. This rapid reproduction leads to large populations where many offspring are produced, increasing the likelihood that some will carry beneficial mutations.

3. Struggle for Survival

• Selective Pressure from Antibiotics: When antibiotics are introduced into an environment (e.g., during treatment of an infection), they create a strong selective pressure. Most susceptible bacteria are killed off, but those with mutations or acquired genes that confer resistance survive. For example, when methicillin is used to treat infections caused by Staphylococcus aureus, only the MRSA strains that have developed resistance can thrive.

4. Reproduction by Better-Adapted Individuals

• Survival of Resistant Bacteria: The resistant bacteria that survive the antibiotic treatment reproduce and pass on their resistance traits to the next generation. Over time, this leads to an increase in the proportion of resistant bacteria within the population. MRSA, for instance, has developed mechanisms such as producing beta-lactamase enzymes that break down beta-lactam antibiotics or altering penicillin-binding proteins to reduce antibiotic efficacy.

5. Passing on Alleles to Future Generations

• Inheritance of Resistance Traits: The alleles responsible for antibiotic resistance are passed on to offspring through reproduction. As a result, subsequent generations of bacteria will predominantly consist of resistant strains. This shift can lead to the emergence of MRSA as a major public health concern, as these strains can spread rapidly within hospitals and communities.