What's Happening to My Body When I'm Sick?

LESSON PLAN

 

Name: George Joseph

 

Title of lesson: Identifying Unknown Microorganisms

 

Length of lesson: 100 minutes (2 days)

 

Description of the class:

                     Name of course: Biology

                     Grade level: 9^th-12^th grade

                     Honors or regular: All levels

 

Source of the lesson:

Information taken from Dr. Pratibha Saxena's BIO 126L Course Packet

 

TEKS addressed:

112.43.1     Scientific processes. The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe, environmentally appropriate, and ethical practices. The student is expected to:

 

(A)  demonstrate safe practices during field and laboratory investigations

 

112.43.4     Science concepts. The student knows that cells are the basic structures of all living things and have specialized parts that perform specific functions, and that viruses are different from cells and have different properties and functions. The student is expected to:

 

(B)  investigate and identify cellular processes including permeability, energy production, transportation of molecules, disposal of wastes, function of cellular parts, and synthesis of new molecules

 

The Lesson:

I.     Overview
This lesson lets students take on the roles of clinical microbiologists in order to identify their unknown bacteria samples. The lesson utilizes data students obtained from the Gram stain lab to help narrow in on their organism.

 

       II.   Performance or learner outcomes

               After this lesson has been carried out, students will be able to:

- inoculate differential media with a bacterium sample

-understand that there is diversity in bacteria metabolism

-identify unknown bacteria by interpreting test results

 

 

    III.   Resources, materials and supplies needed (per class of 24)

• 60 tests tubes with 20 of following:

  • lactose, mannitol, and sucrose fermentation broths

• 3 strains of nonpathogenic bacteria (liquid cultures)

  • Escherichia coli, Micrococcus luteus, Staphylococcus epidermis

• 24 inoculating chucks and wire

• 12 Bunsen burners

• 1 incubator

• box latex gloves (100 gloves each)

• 2 plastic test tube racks

• permanent marker

IV. Supplementary materials, handouts.

-Bacteria Identification Worksheet

 

V. Safety Considerations

 

Engagement

Students will be posed with a situation in which they are clinical microbiologists working in a hospital laboratory. Over the course of the day, a number of patients have come in sick due to bacterial infections. The patients' doctors have requested tests in order to identify the exact species of bacteria that is making each patient ill. The teacher then tells the students that it is up to them to run the tests and find out what the unknown bacteria are.

 

Exploration

Safety Lecture:

Students will be told a set of rules concerning the lab prior to starting. These rules will also be written on the front board throughout the entire lab. Upon entering the class students will be asked to keep their backpacks and other items at the front of the room. Students need to then wash their hands with soap and put on gloves. The gloves must remain on until the end of lab. During the lab students should not eat or drink and should avoid touching their faces. All used items should be properly disposed of. Gloves in the trash can and test media in the biohazard container. Once the lab is completed, students need to again wash their hands with soap before exiting the class.

 

Students are to be split up in the same groups they were in for the Gram stain lab. Each group will be assigned a number. The teacher will provide each group with a test tube rack containing the sample organism used in the Gram stain lab and a set of differential media. Students will be asked to label their test tube rack with their group number using the tape and marker. The teacher will tell the students what is contained in each of the test tube media. Students will then be asked to watch the teacher perform a demo inoculation using the proper technique. Once the inoculating loops have been passed out, students can begin inoculating their media.

After all the groups are finished, the teacher will place the test tube racks in an incubator set at 37 degrees Celsius. The results will be observed after 24 hours.

 

Questions to Ask:

1. Why do you think it is important to identify the exact bacteria causing the infection?

Ans. So that a treatment that works best against that bacteria can be used.

2. Why do you think we are running four tests rather than just one or two?

Ans. Different bacteria could produce the same results and not allow for a unique identification.

3. What information can you use from your Gram stain that could help identify the bacteria?

Ans. The shape (bacillus, coccus), colony grouping (diplo, strepto) and whether it is Gram positive or Gram negative.
At this time prepared slides of the organisms can be shown if students' gram stains did not turn out well.

4. Why can we not just look at the bacteria under a microscope to identify them?

Ans. Since many bacteria share the same shapes, it may not provide enough information for a proper identification. 

5. What do you think will happen to the media you inoculated after 24 hours?

Ans. Varied answers such as color change, bacteria growth, etc.

6. What do you think we can learn about the bacteria from the different media tubes?

Ans. Bacteria that can grow in that media will be able to use that nutrient (mannitol, lactose, or sucrose) for energy.

 

 

END OF DAY 1

 

Students will be handed a "Bacteria Identification Worksheet". The students will look at the media and record any observations on the worksheet. Using the identification chart, groups can determine what their unknown bacteria sample is.

 

Explanation

The teacher can ask the students what happened to each of the test tubes and remind them of each of the test tubes' contents. The discussion should result in the students understanding why their test tubes either did or did not change colors. A yellow color indicates that the bacteria could utilize the sugar (lactose, mannitol, or sucrose). No change in color indicates that the bacteria could not utilize the sugar as a carbon source. The color change is from the acidic by-products, produced by the sugar metabolism, altering the pH indicator.

 

1. What sugars could your group's bacteria metabolize?

Ans. Varied based on group's bacteria sample.

2. How do you know your bacteria can metabolize those sugars?

Ans. The color change from the original media shows that the bacteria utilized the sugar within that media.

 

Elaboration

Students can be questioned on some of the advantages and disadvantages to using this sort of manual identification technique. The teacher should convey the idea that although these tests result in a positive identification, they take time and can become quite tedious when identifying many patient samples. This can lead to some other methods of how bacteria are being identified in today's laboratories, including DNA analysis.

The following website is a very interesting simulation in how DNA analysis is used in identifying bacteria. <http://www.hhmi.org/biointeractive/disease/vlab.html>

 

Evaluation

Students can be provided with an identification chart showing the results for different bacteria. The teacher can show the students a picture of the test tubes with color changes after incubation with an unknown sample. Students will then be asked to identify the bacteria, and then explain what the results mean with regards to the bacteria's metabolism.

 

 

Name:___________________________________________                         Group #:____

 

Bacteria Identification Worksheet

 

1. Record what colors your test tubes are in the table below.

 

Lactose	Mannitol	Sucrose

 

 

2. Were there any changes from the original test tubes?

                                                                                                                                                                                      

 

 

 

 

 

 

3. After performing the Gram stain what kind of bacteria did you find? (circle one)

                        

                                                Gram +               Gram -                                                                                               

 

4. Use the chart below to identify your unknown bacteria.

 

 

Write the name of your organism: ____________________________________________