BI1123
Introductory Biology Lab
Experiment 10
Bacterial Culture
AIM: To streak bacterial colonies on a culture plate.
MATERIALS REQUIRED:
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Petri-dish
Agar gel
Nutrition medium
Burner
Ethanol
Stainless steel loop
THEORY:
A small amount of bacterial culture of mixed types is placed on the tip of an inoculation
loop/needle and streaked across the surface of the agar medium. Streaking it
successively thins out the inoculum enough to separate the microorganisms from each
other.
We normally streak out a second plate using the same loop. These plates are then
incubated to allow the growth of colonies. The fundamental principle used is that a
dilution gradient is established due to streaking, as bacterial cells are deposited on the
agar surface.
Lysogeny broth and nutrient broths media are two popular growth media for bacteria.
PROCEDURE:
1. Sterilise the inoculating loop in the burner by putting the loop into the flame until it
is red hot. Allow it to cool.
2. Take a small droplet of the soil sample and spread it over the first quadrant.
3. Immediately streak the inoculating loop gently over a quarter of the plate using a
back-and-forth motion.
4. Flame the loop again and allow it to cool and dip it in ethanol and then heat it
again. Returning to the edge, extend the streaks into the second quarter of the
plate.
5. Flame the loop again and repeat the procedure to extend the streaks
successively into the third and fourth quarter of the plate.
6. Allow it to incubate for 24 hours at 30 degrees celsius.
OBSERVATION:
We observed bacterial colonies on the agar plate.
RESULT:
Successfully streaked bacterial colonies and observed their growth on an agar plate.