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Teacher’s Guide: Testing Antibiotic Resistance in Bacteria
The Kirby-Bauer Method
Objectives:
The students will:
- observe the effects of selected antibiotics on bacteria
- perform the Kirby-Bauer method for determination of antibiotic sensitivity
- correctly interpret the results of the Kirby-Bauer plate
Prior Knowledge / Laboratory Skills Needed:
- aseptic techniques
- laboratory safety procedures (see lab safety sheet)
- Bunsen burner lighting and safety
- basic structure and function of bacteria
Materials:
- Broth cultures of Staphylococcus aureus, Escherichia coli (Staphylococcus epidermis or other bacteria culture may be substituted)
- paper disksimpregnated with antibiotics (order through major biological supply company, they will come in vials of 50 disks, order 4 – 6 different antibiotics)
- agar plates of Mueller Hinton agar (38g of Mueller-Hinton agar/ 1000ml of distilled water – mix to dissolve and autoclave at 121 degrees Celsius for 15 minutes, pour enough for each group to have 2 plus
additional plates to have on hand if needed, it is best to pour the plates a day or two in advance and then refrigerated)
- sterile swabs (can be purchased or wrap cotton swabs available at the grocery store in aluminum foil and autoclave)
- marking pencils
- forceps
- Bunsen burner
- 70% ethanol in beakers
- metric rulers
- incubator set at 35 degrees Celsius
Instructor Tips:
Background:
Clarify the meaning of antibiotics, sensitive, resistant, agar, and zone of inhibition. Provide examples or make simple sketches to help student understand what the terms mean and how they relate to the
Kirby-Bauer Method.
Problem Statement:
Explain that they will perform the same tests on two different strains of bacteria.
Hypothesis:
Students should write a clear hypothesis. The hypothesis may be outlined or developed as a group for students with limited experience with hypothesis writing.
Materials:
Make suggestions to students about arrangement of their supplies on the lab tables to minimize the possibility of accidents, reinforce aseptic techniques and provide or better results.
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