isolating bacteria 1

7/28/2019 Isolating Bacteria 1

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Materials and Methods

5 sterile agar plate, water sources from the drain and pipe, sterile water, boiled water and

milk, marker pen, wire inoculating loop, and spirit lamp.

Use a marker pen to draw a T on the bottom of your Petri plate of nutrient agar as show

below.

Set the plate you will be streaking so that its bottom is sitting on the bench top and youcan see the T clearly. Rename your Petri plate. Get an inoculating loop and spirit lamp.

Light the spirit lamp. Sterilize the loop by holding its tip in the flame until it turns red.

Wait a minute until the loop cool before placing it into the bacterial source. Place theinoculating loop into one of the liquid cultures and withdraw the loop. Obtain your Petri

plate with agar and lift the lid slightly and remove the lid after complete. Streak the loop

containing the bacteria at the top end of the agar plate moving in a zig-zag horizontal

pattern. Sterilize the loop again in the flame and let it cool before continuing to spread thebacteria. Rotate the plate about 90 degrees and spread the bacteria from the first streak

into a second area using the same zig-zag spread technique. Sterilize the loop again.

Rotate the plate about 90 degrees and spread the bacteria from the second streak into the3rd area in the same pattern. Leave plate in inverted position at room temperature. Record

your observation after 48 hours and until 5 days later.

Repeat with other water sample

Results:

Results and Discussion

Petri plate

The condition of colonies

Colony appearance on

agar plate


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(b) Observe your plates and answer the following questions.

(i) What is meant by colony in bacteriology?

Answer:

Colony is a group of bacteria.

Why do you need to isolate the colony?

Answer:

We need to isolate the colony to individual bacterial (in relative) out of various sources,

to characterize and identify the bacteria present.

(iii) Why was the inoculating loop cooled before inserting into sample?

Answer:

Inoculating loop need to cool before inserting into sample to avoid any organism to be

tested not is killed by the hot wire.

(iv) Why was the Petri plate inverted during incubation?

Answer:

Petri plates need to invert during incubation to avoid the water vapour.

PREPARED BY: MUHAMMAD HAFIZ BIN HUSAIN

(October 12, 2010)

isolating bacteria 1

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