ex. 17

Question 1

antimicrobial agents

Answer 1

kill or inhibit microbes

Question 2

chemotherapeutic agents
aka antimicrobial drugs

Answer 2

are used to kill or inhibit microbes
internally

Question 3

Kirby-Bauer disk diffusion method

Answer 3

1. Label both of your agar plates with your initials and
   species of bacteria. Label one plate “Ex.16” and the
   other plate “Ex.17.”
2. You need to make a lawn of bacteria (see Fig.
   16.1). Dip a sterile swab in the broth culture of
   bacteria and press the swab against the inside wall of
   the tube so it isn’t dripping wet.
3. Starting at the top of the plate, run the swab back
   and forth over the agar until the swab has covered
   every part of the agar’s surface.
4. Turn the plate 90° and run the swab (do not re-dip in
   the culture) over the agar perpendicular to your first
   streaks, again completely covering the entire plate.
5. Turn the plate 45° so that your third set of streaks are at an angle in between the first two sets of
   streaks, again completely covering every square millimeter of agar (you should have streaked across
   every spot on the plate three times, ensuring complete coverage).
6. Run the swab around the outer edge of the agar.
7. Discard the used swab in the biohazard bucket, and repeat steps 2-6 to make a bacterial lawn on
   your other plate
8. Sterilize your tweezers by dipping the ends in the ethanol and flaming them using the Bunsen
   burner; do not leave the tweezers in the flame, remove them as soon as the ethanol is on fire. Wait
   for the fire to burn out, being careful not to drip flaming ethanol on the benchtop.
9. Use the sterile tweezers to obtain a sterile filter paper disk. Dip the disk halfway into a container of
   disinfectant so that the liquid adsorbs up the disk the rest of the way. You should not dip the entire
   disk in the disinfectant or it will become too wet.
10. Gently place the disk containing disinfectant on your agar plate (Fig. 17.1), and label on the
    bottom of the plate the disinfectant used for that disc.
11. Repeat steps 8-11 for 3-4 more disinfectants, spacing the disks as far apart from each other as
    possible and not close to the edge of the plate.
12. Invert the plate and put it in the class tub for incubation (37°C 18-24h).
    Figure 16.1. Making a lawn of
    bacteria using a sterile swab.

Question 4

Know type of media used for Kirby-Bauer disk diffusion

Answer 4

= Mueller Hinton agar

Question 5

Zone of inhibition

Know how to measure zones of inhibition

Question 6

zone of inhibition

be able to
determine most effective/least effective