Antibiotic-Resistant Bacteria: A Simple, Realistic Lab Activity

Every now and then I write a blog post about lab activities that worked in my nonmajors biology class. For example, I have written about reptilobirds (an activity combining meiosis and inheritance), staining banana cells to illustrate digestion in plants, and building models of protein synthesis with candy.

Here’s another topic that nonmajors (and everyone else) ought to know about: the development of antibiotic resistance in bacteria. If you teach biology, you might have learned about antibiotic resistance so long ago that you assume everyone else knows about it too. However, I learned this semester that the misuse of antibiotics is still a real problem. During the week before our “Bacteria and Disease” lab, one of my students came into my office with clogged sinuses. He looked miserable and said that he’d been sick for weeks. He then reported that he had taken some of his roommate’s leftover antibiotics, and although he felt better for a while, he soon got worse again. You did what?! Of course you got sick again! How could you not know that was a bad idea?! I scolded him (more gently than that) and mentally reminded myself that education really does matter.

Photo of Staphylococcus aureus

Staphylococcus aureus. Source: Wikimedia commons

Of course, our lab manual already has an activity that addresses antibiotic resistance. I tried it once or twice. Students used different types of colored pencils (representing various strains of bacteria) to fill in a diagram of lungs in the lab manual. When they tried to erase the pencil marks (i.e., used antibiotics to kill the bacteria), they discovered that not all of the marks would disappear. They were supposed to conclude that antibiotics don’t kill all types of bacteria. The activity was so dull, predictable, and ineffective that I soon abandoned it. For many semesters we’ve showed a video about antibiotic-resistant tuberculosis bacteria instead.

But then I read this article by Eva M. Ogens and Richard Langheim in The American Biology Teacher and I decided to give one of the activities a try. It was appealing because it connects antibiotic resistance directly with something that nearly all students have done: taken a prescription of antibiotics. The simulation uses dice and inexpensive pony beads to model the evolution of bacteria over a course of antibiotics. The pony beads are in three colors to simulate three degrees of resistance to the drugs (we used green for least resistant, yellow for resistant, and red for most resistant).

After a brief introduction, each pair of students is given a petri dish containing a “bank” of 20 green, 15 yellow, and 15 red pony beads. Each student transfers 13 green beads, 6 yellow beads, and 1 red bead to a separate dish, which represents the body and the bacteria currently infecting it. Students are told they are taking antibiotics to fight the infection. They are then instructed to roll the die and record the number in a table. Rolling a 1, 3, 5, or 6 means they remembered to take the antibiotics and get to remove 5 bacteria from the body. Least resistant bacteria die most easily, so green ones are removed first. Once there are no more green ones, yellow ones can be removed. Red ones die last. Rolling a 2 or 4 means they forgot to take their drugs.

Antibiotic resistant beads

The die, “body” (dish with four surviving red beads), bead bank (dish with many beads), and data sheet. Photo by M. Hoefnagels.

Critically, the next step is reproduction: Students add one more of each color bead that has survived in the “body.” This was the only stage at which students tended to make mistakes. Some pairs forgot to do the reproduction part entirely; others put green beads back in the body even after all the least resistant bacteria were supposed to be dead. Both errors change the outcome of the activity, so clear instructions are essential.

Students then repeat the roll/removal/reproduction steps. At each round, they record the number of bacteria remaining until no bacteria remain in the dish. Afterwards, they answer questions on the worksheet. Most of the questions are fairly straightforward, but we were surprised at how many students had a hard time articulating the relationship between bead colors (representing genetic diversity) and the events of natural selection (less “fit” bacteria were eliminated first, leaving the best-adapted to pass their resistance alleles to the next generation).

One of the strengths of this activity is that the bacteria fall into a spectrum of resistance. I’ve observed that even thoughtful students have trouble understanding why antibiotic-resistant bacteria would ever die in the presence of antibiotics. The somewhat-resistant yellow beads and the more-resistant red beads remind students that most bacteria are vulnerable to antibiotics, but some are more resistant than others. Natural selection acts on this genetic diversity.

Note that this simulation lends itself well to graphing activities. One simple idea would be to have students graph the number of bacteria of each color over time. Another would be to collect the data from the entire class and have students graph the relationship between the number of times the antibiotics were forgotten and the number of rounds of antibiotics required to kill all the bacteria.

The writeup in The American Biology Teacher is very good, with one exception: It is difficult to discern from the narrative that 5 bacteria should be removed at each round. We developed a handout that clarifies the instructions and includes a detailed table for recording data. If you want a copy, please leave a note in the comments section and I’ll email it to you.

Reference:

Spreading Disease – It’s Contagious! Using a Model & Simulations to Understand How Antibiotics Work. Eva M. Ogens, Richard Langheim. The American Biology Teacher, Vol. 78 No. 7, September 2016; (pp. 568-574) DOI: 10.1525/abt.2016.78.7.568

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144 Responses to Antibiotic-Resistant Bacteria: A Simple, Realistic Lab Activity

  1. Jill King says:

    Could I please get a copy of your handouts?

  2. Leilagh Boyle says:

    I would love a copy of your handout!

  3. Morgan Gamble says:

    Could I get a copy of your handout?

  4. Kathleen McAuley says:

    Can I please get an copy of your handout? Thank you!

  5. Cheri Chambers says:

    Hi,
    May I please have a copy of your student handout for this activity?

  6. Mette Lillelund says:

    Hi, I would love a copy of your student hand out as well, please. Thanks Mette

  7. Rana Van Voorhis says:

    Hello, Would you mind sharing the hand outs to me as well? Thanks. Rana

  8. Pingback: Another Way to Connect Selection, Phenotype, and Genotype | Teaching nonmajors biology

  9. Kim Forgey says:

    I would love to have a copy of your handout! I used your reptilobird activity with my class this past year and it was very helpful. Thank you so much for your work.

  10. Kelley Aitken says:

    Could you please send me a copy of your handouts? thank you!

  11. Kara Roll says:

    Good afternoon, may I please get a copy of your handouts? Thank you so much!

  12. Julian Roque says:

    Hello, may I please get a copy of your handout? Thank you.

  13. Maggie pedone says:

    Hi! Activity sounds great, could you send a copy?

    Maggieshapiro@gmail.com
    Thanks!
    Maggie

  14. Kerry C Workman Ford says:

    Hello,
    I love your activity and I would greatly appreciate your handouts if at all possible. Thanks!

    Kerry Workman Ford

  15. Heidi McKeen says:

    Hello,
    I would love to have a copy of your handout if possible.
    Thank You!
    Heidi McKeen

  16. Stephen Belsky says:

    May I please have a copy? Thank you. SB

  17. Andy M says:

    This looks like an excellent way to reinforce and reflect on a lesson on resistance in bacteria. Could I please get a copy of the instructions and data table? Thanks for sharing this resource!

  18. Brian Young says:

    Would I be able to get a copy of your handout

    Thanks

  19. Jill Williams says:

    I love this idea! Could I possibly get a copy of the worksheet(s) that accompany this activity?
    Thank you in advance!

  20. AH says:

    What a great activity. Could I please get a copy of the activity?

  21. Niki says:

    Hello, could I get a copy of the lab? This sounds great!

  22. May I have copy of the handout? This lab looks much simpler than the one I have and am trying to simplify. Thanks!

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