Bacteria and antibiotics Experiment
Precautions
-
Disposable aprons and gloves
Dispose of waste (aprons, paper towel etc) in specified rubbish bag
Disinfect benches after experiment is complete
Don’t open sealed agar plates when observing results on day 2
Method
Part A – Manufactured antibiotics
1. Label the base of an agar plate, around the edge, with the your group name and the name of the
bacteria you are using (either S. albus or E. coli, your teacher will advise you)
2. Using a disposable inoculation loop, streak the agar plate with the bacteria using the method
below
3. Place the mastring on the agar plate, using the forceps
4. Put the lid on the petrie dish and seal with sticky tape
5. Place in the incubator, lid down
Part B – Natural antibiotics
Repeat steps above, but rather than a mastring, place several discs of filter paper on the agar plate,
soaked with natural antibiotics (eg. honey, tea tree oil, garlic).
You will need to write on the base of the plate, which substance is where.
Results
Without removing the lid, you will use a ruler to
measure the ‘zones of inhibition’ around each
antibiotic disc. Use the ‘annular radius’ at the
measurement you record in the table.
Record the results in the table over the page.
Antibiotic
Zone of inhibition for
E. coli (mm)
Zone of inhibition for
S. albus (mm)
Discussion
1. Which antibiotic worked best on E. coli?
2. Which antibiotic worked best on S. albus?
3. What are the benefits of having several antibiotics that can kill a bacterial species?