You'll be testing the effects of various compounds on bacterial growth. For both the antiseptic/disinfectant experiment, and the antibiotic susceptibility experiment, you'll be placing paper disks containing these compounds on these plates, then measuring the effect of the compound on bacterial growth at the next lab. To ensure that you are testing, you need to make sure that these paper disks are handled properly:

The disks should be placed on the plate ______ the plate with the bacterial culture.
Use _ to place the disks on the plate.
Make sure the disk is ___ the surface of plate.
after before forceps wiped with alcohol

an alcohol swab

your fingers

a sterile swab

forceps

buried in

resting on top of

1. The antibiotic disk is gently placed directly above the plates and spread across the plate to allow easy sectioning of the disk - since an antibiotic disk contains different antibiotics whose rate of effect we intend to measure against a particular bacteria. After sectioning, the antibiotic in the section with the largest zone of inhibition is considered more effective against the bacteria.

2. The forceps must also be sterilized before using it to pick-up the disk to avoid contamination. Forceps are used because it is easily sterilized and safer to use - since we are most likely dealing with an infectious agent - using the fingers will not only contaminate the plates, but it could equally be harmful to the handler.

3. It is necessary that the disk must be pressed onto the surface of the plate - to enhance the interaction between the plate and the antibiotics on the disk so as to use the antibiotics optimally.