Attack of the Superbugs!
Lesson 3 of 4
Objective: Using antibiotics resistance as a model, the student will explain how living things adapt for optimum survival through natural selection.
By studying how antibiotic resistance is developed, students learn about natural selection. Here is an overview of what students will learn today.
Poll the class to determine
- if anyone has taken antibiotics.
- if anyone knows someone who taken antibiotics
- if anyone know someone who has had MRSA.
Briefly explain to the students the purpose of each station. Then explain to the students that they can start at any station for this exploratorium. Each student group should be assigned a starting station. Set a timer and inform students when the timer goes off, student groups move to the next station. Directions describing the activity should be placed at each station.
Students should use the following handout with this exploratorium.
(Note: Typically, I will have students work in groups of four (depending on class size) for this exploratorium. For very large classes, more than one of each station could be set up. This is a modification of the classic antibiotic resistance lab. It is now recommended that high school labs no longer complete the traditional lab due to the problem with the development of antibiotic resistant bacteria. See my teacher reflection for more explanation of when and why I use an exploratorium in my classroom.)
At this station, students will make a bacterial lawn. This station will help students better understand part of the process involved in determining the antibiotic resistance of certain bacteria without actually making antibiotic resistant bacteria. Making a bacterial lawn is the first step in many bacterial protocols. Once they have completed making the lawn, they should sketch the appearance of the surface of the plate in their lab notebook or the worksheet that is provided.
Since a 24 hour period is required to grow a bacterial lawn, students check for bacterial growth in the next class period. Tomorrow students will make a sketch of the appearance of the surface of the plate in their lab notebooks. You may also use the student handout for the exploratorium.
(Note: I have my students check for growth during the opening portion of the next class period.)
For this station, students will use a Vis-a-Vis marker to divide the plate into sections and indicate where the zones of inhibition are on the plate. Next they will measure the zone of inhibition to determine to which antibiotics the bacteria on the plate are resistant. They will fill in the data table in their student notebook. See student handout from the previous section for more detailed instructions.
Note: To differentiate, the teacher can limit the number of plates that students need to analyze. Also, to make the lab more realistic, the teacher could cut out the plate and place it into a disposable petri dish. The petri dish can be sealed with parafilm.
For this station, each student group will make a streak plate for this station. Streak plates will need to be incubated over night in an incubator at 30 degrees F.
Making a streak plate is the first step in isolating bacteria in many bacterial protocols. This station will help students better understand how streak plates are used in part of the process involved in determining the antibiotic resistance of certain bacteria.
(Note: For those unfamiliar with the streak plate protocol, it is described here.)
Use this rubric to evaluate student performance at this station.
Students should read the scenario at the station to determine how the drug resistant bacteria were developed over several weeks.
There were six antibiotics tested during this experiment: ampicillin (Amp), tetracycline (Tet), streptomycin (Strep), rifampicin (Rif), kanamycin (Kan), and chloromphenicol (Chl).
- By the end of the experiment, 262 lines of bacteria were grown.
- 17 lines were resistant to Amp, Strep, and Kan.
- 1 line was resistant to Amp, Chl, Kan, and Strep.
- 16 lines were resistant to Amp and Strep.
- 11 lines were resistant to Tet.
Determining the percentage of bacteria that were resistant to one type of antibiotic, 2 types of antibiotic, 3 types of antibiotic, and 4 types of antibiotic. Make a pie chart to help display your findings.
Refer to the student work sample for a more detailed explanation.
This station is based on a student study, Antibiotic Resistance in E. coli from the University of Virginia Biology Department. This entire study can be found here.
Using the graph found on Exploring Resistance Map website, have students explore what has occurred concerning drug resistance with bacteria causing urinary tract infections (UTI) and soft tissue infection. Have students write a summary in their lab notebooks.
(Sample summary: Between 1999 and 2010, the Urinary Tract Infection Drug Resistance Index (UTI-DRI) increased by 35%. Following an initial decline from a baseline of 16.8 in 1999 to 15.1 in 2001, the UTI-DRI increased steadily for eight years, reaching 22.8 in 2010.)
Next, discuss the mechanism of horizontal gene transfer with students as an explanation of how drug resistance occurs. Finally, discuss with student how antibiotic resistance might be an excellent adaptation for survival in bacteria. Ask students how might antibiotic resistance be evidence to support evolution or in other words why would it be beneficial for bacteria to have antibiotic resistance?
- Because there has been natural selection on bacteria.
- Because antibiotic resistance gives bacteria the ability to survive and a reproductive advantage
- Because the bacteria make enzymes that help break down the antibiotic.
Homework: Students should listen to the podcast Antibiotic-Resistant Bugs Turn Up Again in Turkey Meat and write a current events summary. (Note: I like having my students listen to these type of podcasts because they show students that the content they are learning in the classroom relates to real life situations. NPR's podcasts are designed for students because they are relevant and short. I believe they are a perfect extension activity for my class.)