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How Antibiotic Resistant Bacteria Take Over

Summary

Active Time
20-30 minutes
Total Project Time
20-30 minutes
Key Concepts
Microbiology, medicine, bacteria, antibiotics, antibiotic resistance
Credits
Svenja Lohner, PhD, Science Buddies
How Antibiotic Resistant Bacteria Take Over – STEM activity

Introduction

Have you ever had to take antibiotics? Your doctor probably told you to finish taking all the pills even if you felt better after one or two days. But why is that? Why shouldn't you stop taking antibiotics as soon as you feel better? You might be surprised to hear that if you do, you might contribute to the creation of antibiotic resistant "superbugs!" Find out how these superbugs can develop in this activity by rolling dice to model how different bacteria respond to an antibiotic treatment.

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Materials

  • Six-sided dice (20 total. 15 of one color, 5 of another color.) Note: Alternatively, you can use an online dice roller.
  • Paper
  • Pen
  • Graphing paper (optional)

Prep Work

Choose a large, flat work area where you can roll all your dice without them falling off the table.

Instructions

  1. Make two piles with the two different-colored dice. In your model, each die represents one bacterium.
    Think about:
    Which pile do you think represents the non-resistant bacteria, and which one the more resistant bacteria?

  2. Write on your paper which color represents which bacteria. (Tip: In nature, non-resistant bacteria are most abundant. Bacteria that are more resistant to antibiotics are luckily still less in number.)
  3. In your simulation, each roll of the dice corresponds to taking one dose of antibiotics. More resistant bacteria survive the antibiotics when the roll outcome for these dice is a 2, 3, 4, 5, or 6. Non-resistant bacteria survive when the roll outcome for these dice is a 6.
    Think about:
    How are the survival probabilities different for the non-resistant versus the more resistant bacteria?
  4. Mix all your dice together and roll them. Separate the rolled dice into a "surviving" pile and a "died" pile based on the roll outcome of the individual dice and the rules mentioned in step 3.

  5. Set all the dice in the "died" pile aside. They will not be used anymore. Count how many dice of each color are in the "surviving" pile and record your results on a piece of paper.
    Think about:
    How many bacteria survived? How many of the more resistant or non-resistant bacteria died?

  6. Repeat steps 4 and 5 until no dice are left. Record your results every time you roll the dice.
    Think about:
    How many rolls does it take to kill all of the more resistant bacteria? Do the more resistant bacteria survive longer or for less time compared to the non-resistant ones? Why do you think this is the case?

What Happened?

Were you able to kill all the bacteria? Probably yes, but it might have taken you some rounds of rolling the dice to do so. You probably noticed that the "normal," or non-resistant bacteria got killed off pretty quickly. As they only survived in your model when the roll outcome was a 6, and with 6 possible numbers on the die, the probability for them surviving one roll (representing one dose of antibiotics) was only 1 out of 6, which is 16.6%. It shouldn't have taken more than 3 or 4 rolls to eliminate all non-resistant bacteria.

However, the more resistant bacteria in this model have a survival probability of 5 out of 6, or 83.3% for each roll, as they survive when a 2, 3, 4, 5, or 6 is rolled. This means that it should have taken much longer to kill all the more resistant bacteria. Even though they start out at a much lower number than the non-resistant bacteria, after 3-4 rolls, they should be the only ones alive. It probably took you up to 10 or even more doses of antibiotics (or dice rolls) to kill them all.

This is exactly what happens in real life with the real bacteria. One dose of antibiotics is very efficient in killing off bacteria that can't resist the effects of the drug. However, bacteria that can defend themselves against the antibiotics are able to survive the first dose and it will take several doses of treatment to kill them. Keep this in mind for the next time you have to take antibiotics. Take them responsibly, so you can avoid the creation of superbugs!

Digging Deeper

Bacteria are microscopic organisms that are found everywhere. They are even inside and outside our bodies! Most bacteria are harmless to humans, but some can cause serious illnesses. Any microorganism that makes us sick is called a pathogen. Antibiotics are drugs that are used to kill pathogens responsible for a bacterial infection such as strep throat or ear infections. Before the discovery of the first antibiotic, penicillin, in 1928 by Alexander Fleming, people frequently died from minor wounds and infections (things we might think of as trivial injuries, like a scraped knee). Today, penicillin is estimated to have saved between 80–200 million lives.

However, many antibiotics have lost effectiveness because bacteria have become resistant to them over time, generating bacteria that are known as "superbugs." Antibiotic resistance means that the bacteria have gained the ability to resist the effects of the drug that used to kill them. Antibiotic resistance is created when the bacteria's genetic material mutates in a way that makes them less susceptible to the drug or allows the bacteria to deal with the antibiotic before it can do any harm. Such mutations can happen when bacteria are unnecessarily exposed to antibiotics and can be caused when people take antibiotics when they don't need them, improperly dispose of antibiotics, or take antibiotics in the wrong time period during a bacterial infection.

An antibiotic treatment kills non-resistant bacteria pretty quickly and selects for the bacteria that are more resistant to the drug. The surviving bacteria are more likely to become antibiotic resistant and replace the bacteria that have been killed. This selection is based on the fact that not all bacteria are the same, which means that some bacteria can be more resistant to a certain antibiotic than others. This also explains why it is not enough to take antibiotics just once when you are sick. As some bacteria have better strategies to resist the drug, they will survive one dose of antibiotics and it will take more doses to kill them.

There is little research on what the perfect treatment time for antibiotics is, especially as it is also very dependent on what bacteria are causing the illness. However, scientists agree that either taking antibiotics for too short or long a time increases the risk of creating antibiotic resistances.

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For Further Exploration

  • Increase the number of dice for each bacteria group or change the ratio of more resistant versus non-resistant bacteria. How does this change your results?
  • Use graphing paper to graph your results. On the horizontal axis, write the number of doses (or how often you have been rolling the dice), and on the vertical axis graph the number of survived bacteria after each dose. How do your graphs for the more resistant versus non-resistant bacteria compare?
  • Change the rules in your model and change under what conditions (or roll outcomes) the bacteria survive. Alternatively, you can add 10 "mildly resistant" bacteria represented by 10 dice of a third color to your bacteria mix. Let these bacteria only survive when the roll outcome is 4, 5, or 6. What results do you get with three different kinds of bacteria?

Project Ideas

Lesson Plans

    Lesson Plan Grade: 6th-8th
    If your doctor prescribes antibiotics, why do you have to take them for several days and not just once? Why do you need to finish taking them even if you feel better? If you do not follow the doctor's orders, you might contribute to the creation of antibiotic-resistant "superbugs"! In this lesson, your students will roll dice to model how bacteria respond to treatment by antibiotics, and find out what happens if treatment is stopped too early. Read more
    NGSS Performance Expectations:
    • MS-LS4-4. Construct an explanation based on evidence that describes how genetic variations of traits in a population increase some individuals' probability of surviving and reproducing in a specific environment.
    • MS-LS4-6. Use mathematical representations to support explanations of how natural selection may lead to increases and decreases of specific traits in populations over time.

Careers

Career Profile
Microorganisms (bacteria, viruses, algae, and fungi) are the most common life-forms on Earth. They help us digest nutrients; make foods like yogurt, bread, and olives; and create antibiotics. Some microbes also cause diseases. Microbiologists study the growth, structure, development, and general characteristics of microorganisms to promote health, industry, and a basic understanding of cellular functions. Read more
Career Profile
Physicians work to ease physical and mental suffering due to injury and disease. They diagnose medical conditions and then prescribe or administer appropriate treatments. Physicians also seek to prevent medical problems in their patients by advising preventative care. Ultimately, physicians try to help people live and feel better at every age. Read more
Career Profile
Have you ever heard the expression "Prevention is the best medicine"? Prevention is the fundamental work of all health educators. They attempt to prevent illnesses or diseases in individuals or entire communities through education about nutrition, exercise, or other habits and behaviors. Health educators present scientific information in ways that their audience can relate to, and are sensitive to cultural differences. They are the cornerstone of the public health system, improving health and… Read more
Career Profile
Pharmacists are the medication experts. They advise doctors, nurses, and patients on the correct drug dosage for a patient's weight, age, health, and gender; on interactions between drugs; on side effects; on drug alternatives; on costs; and on ways to give drugs. They also dispense drugs at pharmacies, according to prescriptions, checking for dangerous drug interactions, and educating patients on how to take drugs, what reactions to watch out for, and how long it should take for drugs to work. Read more

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