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Student Guide: Testing for Antibiotic Resistance in Bacteria - The Kirby-Bauer Method
Background:
There are many different antibiotics available today. You may even be taking an antibiotic right now! Scientists are working to discover and develop new antibiotics all the time.
Scientists need to find out whether different types of bacteria are sensitive or resistant to each antibiotic. If the bacteria are sensitive to an antibiotic then the antibiotic will either kill the bacteria
or prevent its growth. If the bacteria are resistant to an antibiotic then the bacteria will grow normally.
One method to test for bacterial sensitivity and resistance to a particular antibiotic is a procedure called the Kirby-Bauer Method. In this method, an agar plate is covered with a bacterial culture then paper
disks containing the specific antibiotics are placed on the agar plate. After the agar plate is incubated, the zone of inhibition around each disk is observed and measured. The zone of inhibition is the
clear area around the disk in which bacteria were not able to grow. Scientists use the size of the zone of inhibition to determine whether the bacteria are sensitive or resistant to the antibiotic. For
example, zones of smaller size or no zone at all show that the bacteria are resistant to the antibiotic. If the bacteria are sensitive there will be a definite clear zone and the bigger the zone the more
sensitive the bacteria is to the antibiotic.
Problem Statement: Are Staphylococcus aureus and / or Escherichia coli bacteria resistant to various antibiotics?
Hypothesis: Write your hypothesis.
Materials:
- 2 agar plates
- 2 sterile swabs
- antibiotic disks
- marking pencil
- broth cultures of E. coli and S. aureus
- forceps
- alcohol
- Bunsen burner
- incubator
- metric ruler
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