Biology : Unit #3 - Bacteria : Lesson #3

Attack of the Superbugs!

Objective: Using antibiotics resistance as a model, the student will explain how living things adapt for optimum survival through natural selection.
Standards: W.9-10.2d W.9-10.9 RST.9-10.1 MP2 MP3 HS-LS4-4 SP4 SP6 XC-CE-HS-1
Subject(s): Science
60 minutes
1 What Students Will Learn in this Lesson - 1 minutes

By studying how antibiotic resistance is developed, students learn about natural selection. Here is an overview of what students will learn today.  

2 Setting the Stage: Explanation of the Exploratorium - 5 minutes

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.

Then, introduce the essential vocabulary for this lesson.  Using the Frayer method, define streak plate and bacterial lawn.

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.)

Maintaining Order in the Lab
Classroom Setup

I use exploratoriums throughout this unit so that we can cover a great deal of information in a short period of time. We have some equipment for culturing bacteria, but not enough for an entire class to use at once. To solve this problem, I set up unique individual stations at which a small group of students can work. 

My students are first introduced to the exploratorium/station concept when they are freshmen in my Earth Science class. They learned that they will have a set period of time at each station. They need to be aware that when the timer goes off that they need to rotate. They can always come back to the station when everyone is done and finish anything they have not quite completed. In addition, if I only plan to have an exploratorium up for one day.  I will allow students to come to the room at certain times (Learning Academy and Seminar) so they can finish any portion they do not have complete. This method has work best for me since I teach all of the science classes and all of these classes are considered lab classes. I need to keep a tight schedule when students are conducting labs. My room is not very large and if I try to set up more than one lab in a day, it can be very chaotic. We have to be careful because it is during the chaotic times that equipment gets broken or people get hurt.   

When designing an Exploratorium, I keep several criteria in mind. First, the stations need to be somewhat interactive. Students need to be doing something. Secondly, set-up and clean-up need to be quick and easy. This year because of our numbers, I am only teaching one section of each of my classes. Therefore, by the end of the period, all equipment needs to be put away if another lab in another class is planned. Finally, exploratorium need to teach necessary skills that students can apply later. They need to allow students to analyze research or data sets that can make their understanding of a concept more sophisticated. 


3 Station 1: Creating a Bacterial Lawn - 8 minutes

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.)


4 Station 2: Reading Results from the Disk Diffusion Method - 8 minutes

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.

There are six plates that can be used with this lab.  They should be labeled Plate 1Plate 2Plate 3Plate 4Plate 5, and Plate 6.  Plate 7 can be used for testing purposes.  

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.  

5 Station 3: Making a Streak Plate - 8 minutes

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.  



6 Station 4: Interpreting Results from Streak Experiment - 8 minutes

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.   

7 Putting it All Together: Current Trends in Resistance - 8 minutes

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?  

Possible answers:

  • 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.)