Antibiotic Resistance: A Growing Threat

Target Audience: 10th Grade Biology NGSS Performance Expectation: HS-LS4-4 - Construct an explanation based on evidence for how natural selection leads to adaptation of populations. SEP: Constructing Explanations and Designing Solutions DCI: LS4.C: Adaptation CCC: Cause and Effect

The Phenomenon

A patient is diagnosed with a severe bacterial infection and is prescribed a 10-day course of antibiotics. For the first few days, the patient feels much better as the symptoms subside. However, around day 7, the patient starts feeling worse again. The doctor prescribes a second round of the same antibiotic, but this time, it has no effect on the infection.

Why did the antibiotic stop working?

Part 1: Initial Ideas

  1. Based on your current understanding, write down a hypothesis explaining why the antibiotic was initially effective but later failed to cure the patient’s infection.
  2. What role do you think the bacteria themselves played in this change?

Part 2: Simulation Investigation

Open the Antibiotic Resistance Simulation.

Baseline Observation

  1. Set the Mutation Rate to 5% and Mutation Impact to 10.
  2. Click Reproduce a few times to simulate the bacteria population growing and changing over several generations without any antibiotics.
  3. Observe the average resistance level. How does the resistance level of the population change when no antibiotics are present?

Introducing the Antibiotic

  1. Now, set the Antibiotic Strength to 50.
  2. Click Apply Antibiotic once. What happens to the population size and the average resistance of the surviving bacteria?
  3. Click Reproduce a few times to let the surviving bacteria repopulate. What do you notice about the resistance of the new generation of bacteria compared to the original population?

The Role of Mutation

  1. Click Reset Simulation.
  2. Set the Mutation Rate to 0%. Try growing the population and applying antibiotics.
  3. How does the absence of mutation affect the population’s ability to survive the antibiotic? Compare this to your observations in the first trial.

Part 3: Making Sense of the Evidence

  1. Analyze the Data: How did the distribution of traits (resistance level) in the bacterial population change before and after the application of the antibiotic? Use specific data (average resistance percentages) from the simulation to support your answer.
  2. Identify the Cause: Did the antibiotic cause the bacteria to mutate and become resistant, or did it act on variations that already existed in the population? Explain your reasoning based on the simulation results.
  3. Construct an Explanation: Using the evidence you gathered from the simulation, construct an explanation for the phenomenon described at the beginning. In your explanation, explicitly connect the four factors of natural selection:
    • The potential for a population to increase in number.
    • Heritable genetic variation in the population.
    • Survival under environmental pressure (antibiotic application).
    • The proliferation of individuals with advantageous traits.