PAG07 = MICROBIAL TECHNIQUES Flashcards
When growing bacteria what are the sterile techniques used?
Wash your hands and disinfect your work area.
● Have Bunsen Burner on to sterilise the air and prevent air-borne
microorganisms settling.
● When opening the bottle of broth, pass the neck over the Bunsen Burner flame to
prevent the microorganisms in the air entering the bottle.
● Only open a petri dish enough to allow you to introduce your desired organisms.
● All equipment should be sterilised by passing it over the flame before and after use.
How do you add antibiotics to petri dishes?
Using a sterile pipette, add the same volume of each antibiotic to a different
Petri dish. Antibiotics used could include: penicillin, ampicillin, etc.
How do you add the bacteria to the dish?
Dip an inoculating loop in the broth
Spread a streak of broth over the agar surface, then close the Petri dish, and tape it
shut. Repeat for the remaining Petri dishes.
How do you control the experiment?
Two petri dishes with no antibiotic should
also be inoculated and two uncultured petri dishes should be added to act as controls.
What do you do to the plates after adding bacteria?
Label each petri dish.
5. Place the petri dishes in a warm incubator.
6. The plates should be incubated upside down to stop condensation forming on the lid
from dropping onto the agar.
7. Leave all the plates for the same amount of time (e.g. a day) then observe the results.
How do we observe the results?
If bacterial growth has occurred, colonies of bacteria on the surface of the agar should
be seen.
9. Count the number of colonies that have formed on each plate and record results in a
table.
10. Work out the mean number
11. If colonies overlap, make serial dilutions with the bacteria broth so more manageable.
