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.
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 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.
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
Send me a copy please
I’ll email you
I’d also love a copy of the questions students answer afterwards.
No prob. I’ll send it your way
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Can you email it to me aswell!
I emailed you!
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Of course. I just emailed it to you!
If you could send me a copy, I would really appreciate it!!
Yes of course. I’ll email you soon.
I would love a copy!
Oops, sorry, I didn’t notice this comment until now! I’ll be sending you the materials shortly.
I’d also love a copy
I will send it to you now.
I’d love to receive a copy. Thanks.
No problem. I’ll email you in a few minutes.
Love a copy to review! Thanks!
Hi, I just emailed it to you. I hope it is useful!
Hi, could you send me a copy?
Hello, it’s on its way!
I would like a copy please! Thank you 🙂
You bet! I’ll send you an email shortly.
Can you please send me a copy ? Thanks
Yes, I’ll email you
I too would love a copy if possible!
No problem. I’ll send it to you soon
Hi, could you please send me a copy ? thanks 🙂
Hi, of course. I’ll send it to you now!
Thanks so much for the article. I would appreciate a copy. Thanks!!
Sure thing. I’ll email you!
Would it be possible to get a copy of the worksheets for this activity? I’d love to do this with a group of homeschooled students!
Of course. I emailed you a moment ago
This looks great- would you mind sending me a copy?
Thanks!
Hi Erin, I’ll send it to you in a few minutes!
I would love a copy!
Great! I’ll send it to you soon
Would you mind sending me a copy of the worksheets for this activity?
I’d love to do this with a group of homeschooled students!
Thanks for sharing your great ideas.
I’ve emailed it to you. So sorry for the delay.
I would love a copy of your activity. Thank you!
I’m finally getting around to emailing this to you! Check your inbox soon.
This looks great, would you mind sending me a copy?
Hi Shana, I emailed you!
Love the lab! Could I get a copy of the materials?
Of course! I just emailed you.
I would love a copy as well if it is still available. Thank you!
Not a problem. It should be arriving in your inbox shortly
I would love a copy of this as well. Thank you.
Hello,
Can I please have a copy of the activity? Thank you
Yep! I’ll send it now.
This looks like a great activity! I’d love a copy if it is still available.
No problem, I’ll email you!
Hello, PLEASE, PLEASE share the worksheet and copy of the activity with me. I have learning support classes and this would be perfect. Thanks so much!
Of course! Sending it now
Hi again, gmail says that the email address you have saved in WordPress doesn’t exist. Where would you like for me to send the document?
Please send me a copy of the student activity. Thank you
You bet. Emailed it a moment ago.
this is awesome. I would love a copy.
I sent it to your inbox a few moments ago
This sounds lovely! Would you mind sending it to me?
I just sent it your way!
May I please have a copy as well? Thanks in advance!
I’ll send it in a moment 🙂
Hi! If you could send me your handout I would really appreciate it!
Sure thing. I’ll email you in a moment.
I would like to use your materials please. Thanks for creating this!
Yep! I sent it to you.
You may as well post this somewhere, because this is great! Would love a copy of it if you got one! 🙂
Please email me a copy when you can. Thank you so much!
Yes, I’ve emailed it over to you now. Enjoy!
Hi! I’d love a copy of your lab materials. Thank you so much!
I would love a copy please!
Hello,
I would love a copy please
You bet! I’ll email it to you shortly. Sorry for the delay.
Of course. I sent it to you a few minutes ago
Could I have a copy as well
Certainly! I’ll send them to you right away. Sorry for the delay in replying; your comment fell through the cracks.
I would love a copy please
I’ve sent it your way!
May I have a copy, please?
Yes! I’ll email you
Could I have a copy as well. Thanks.
Of course. Sending it now
Thank you so much. I got your email with the instructions and worksheet.
This sounds great! Could I please have a copy? Thank you!
Sorry for the delay. I sent it your way!
I’d love a copy if you can send it my way!
Of course. I emailed you!
May I please have a copy?
I just emailed you!
Thank you, I don’t see the email.
I sent it to a ‘schools.nyc’ email address. Let me know if it didn’t come through and I’ll send again.
We are trying to redo our general biology labs for next semester and I would really like to include this activity. Could I get a copy please?
Of course. I will email you in a few minutes.
I would love a copy for my class!
Of course! I’ll email you in a few minutes
I teach high school biology and I would love a copy of this lab. Thank you.
Sorry we missed this comment. I’ll send it to you soon!
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I’ll send it your way