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Health Science and Medical Technology

Lesson Plan Originally Created By: Daniel Raffa

How to Make LB Agar

Part of Unit: Laboratory Techniques and Safety

Lesson Plan Overview / Details

LB (Luria-Bertani) Agar is an essential media in using for bacteria growth.  This lesson has students solve the ratio equation for how much LB agar to measure out.  Then students dissolve the agar using a hot plate and store it in a media bottle.  Finally students place their media bottle in an autoclave to sterilize.

Lesson Time

Two Class Periods
50 Minutes

Objectives and Goals

  • Students will learn proper procedures in using lab equipment to obtain a sterile environment.
  • Students will figure out the amount of LB agar to measure out using using a ratio equation with the directions on the bottle.
  • Students will analyze the success of their sterile technique by looking for contamination.

Activities in this Lesson

  • This is a great start to the lesson by having it play as the students walk in.  After the song or video you can ask students if they recgonize the original song.  This is done by a professor at UC Davis.  Ask the students what they know about contamination of food and water.  That it is a harmful bacteria that grows and gets us sick. Then explain to students how Biotechnology uses bacteria to make medicines for us.  It is very important that scientist have only the bacteria of interest growing.  Explain to students we could use chicken to grow our bacteria but there is standard media that is used to grow bacteria.  Our media, which is called LB Agar must be sterlized before we use it.

    Resources and Materials

  • The Howard Hughes Medical Institute has excellent resources for teachers and students.  The link I have provided is from their 2000 and Beyond: Confronting the Microbe Menace.   Click on Lecture 2 - The Microbes Strike Back. 

    Number 5 is an excellent Demo to help students understand microbe size.  I do this demo with my students rather than showing video. 

    Number 7 and 8 you can use as a hook for students on the number of bacteria in and outside your body. 

    Number 11 is a great video to show how quickly bacteria grow on a petri plate.   This leads into our activity of how to make the media "food" for bacteria to grow. 

    Resources and Materials

    • HHMI- Howard Hughes Medical Institute [ Go to Site ] This is the general resource site on microbes.
    • Microbes Lecture Video (Flash) [ Go to Site ] This is the specific video referenced in the above activity.
  • Show students the LB agar stock bottle and explain that this is a powder that we must get dissolved into a liquid.  To do this we must do a ratio problem.  Have a student read the directions on the bottle.  Explain to students that M1 and V1 are the Mass and Volume on the stock bottle.  V2 is the volume that we want to make (desired).  We need to solve for M2. Model a practice problem then have students practice one in the lab.  Students then check their work with their partner then confirm with me. 

  • This movie was made by some of biotechnology students.  It is a good to use as an anticipatory set, review tool if a student is absent, or as a modeling activity before they start the lab. 

    Have a beaker and a hot plate in the front of the classroom and explain to students that setting the heat above 7 will cause the agar to boil over and that stir over 4 will cause your agar to evaporate rapidly. 

    Resources and Materials

  • Have students work in groups in two.  Please stress the importance of wearing goggles and hot hands.  Students must watch their beaker on the hot plate, this is not a time for them to do other things.  Agar dissolving takes about 8-10 minutes.

    Resources and Materials

  • Groups of 2 Group Work

    As students are working, circle the classroom ask students:

    Is your glassware clean?  Is your table top clean?  What things are you doing to monitor safety of you, your partner, and the classroom?  Did you clean your hands before you started?  Why would this be important?

  • In order for students to get a grade for the first period they must show me their media bottle with a jiggle top and a piece of autoclave tape on the top.  Have student's put it into the classroom. Tell students to clean their work area.  Common things left dirty are weigh boats left out, weigh balances with agar on them, and beakers in the sink. 

Assessment

Assessment Types:
Demonstrations, Observations,

Teacher will grade students on their participation of working in a group to make LB agar.

Completing production of LB agar on a Friday is ideal because you can store over the weekend.  Students can then come back on Monday and the ones who have contamination will have strong results.  Allows for a good discussion on proper technique.  Students must produce a 250 mL media bottle with 125 mL of LB agar in it.  Teacher will show how correct volume, proper labeling and no contamination is successful completion.  Students will self grade themselves by writing a reflection in their scientific notebooks.