First 363 words of the document:
Biology Unit 4
Topic 6: Infection, Immunity and Forensics
18. Describe how to investigate the effect of different
antibiotics on bacteria.
You will need:
Agar plate seeded with a known bacterium
Bench spray of disinfectant, 1% Virkon or equivalent
Soap or handwash
Mast ring or antibiotic-impregnated paper discs
1. Wash your hands with the soap or handwash. Spray the working area thoroughly with the
disinfectant spray. Leave for at least 10 minutes, then wipe with a paper towel.
2. Work very close to a lit Bunsen burner. Prepare an agar plate seeded with bacteria. This may
have already been done for you. Label the Petri dish on the base at the edge with your
name, the date and the type of bacterium it is inoculated with.
3. Flame the forceps and then use them to pick up an antibiotic disc or Mast ring. Raise the lid of
the Petri dish and place the Mast ring firmly in the centre of the agar; if individual discs are
used they will need to be spaced evenly around the dish.
4. Tape the dish securely with two pieces of adhesive tape (but do not seal it completely),
then keep it upside down at room temperature for 48 hours.
5. Wash your hands with soap or handwash and clean the bench again using the Virkon spray.
6. After incubation, look carefully at the plate but do not open it. When bacteria have grown
the plate will look opaque, but there the antibiotics have inhibited growth, clear zones called
inhibition zones will be seen. Measure the diameter of the inhibition zones in mm and use
this information to decide which antibiotic is most effective at inhibiting the growth of the
7. Collect data from other members of the class who used the other bacterial cultures
8. Write a brief report of the results, comparing the different antibiotics and the effects on the
different bacterial cultures
Text Book: p.107