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Using Streak Plate Technique to Isolate Single Colonies, Study notes of Microbiology

University of Maryland Eastern Shore Microbiology

The streak plate method allows isolation of a single colony from a bacterial culture by splitting the plates into quadrants and diluting the bacteria ...

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2021/2022

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Name ______________________________________ Per_______________

Using Streak Plate Technique to Isolate Single Colonies

OVERVIEW

Most microbiological work requires that a culture be started form a single colony. A colony is a single

bacterium that has multiplied on a solid medium into millions of clones of itself and looks like a round visible dot

on the solid medium. The streak plate method allows isolation of a single colony from a bacterial culture by

splitting the plates into quadrants and diluting the bacteria repeatedly as the loop is streaked through each

quadrant. Individual colonies of bacteria are referred to as colony forming units (CFUs), and these indicate a

mass of individual cells of same organism, growing together. However, it is important to remember that CFU is

not a measure for individual cells or spores as a colony may be formed from a single or a mass of cells or

spores.

OBJECTIVE

Isolate single colonies on a LB agar plate from a lawn of bacteria.

PROCEDURE

Step 1: Obtain the proper media plate for your bacterial sample, such as an LB agar plate; label the bottom

with your name, date and bacterial species, and set up your materials in a sterile environment such as a clean

bench top.

Step 2: Aseptically transfer a very small amount of your sample to the edge of your agar plate. Deposit your

sample (gathered with a sterile loop from the other agar plate) on the outer edge of the new agar plate. Use

your sterile loop to gently spread out the sample in a zig-zag manner along one quadrant of the plate from the

edge inward. Do not break the surface of the agar!

Step 3: Rotate the plate 45 degrees, and drag the loop gently through your first quadrant (only once).

Continue to streak the second quadrant of your plate in a similar zig-zag manner from the outer edge of the

plate inward.

Step 4: Rotate the plate 45 degrees, and drag the loop through the second quadrant once. Zig-zag streak the

third quadrant of your plate from the edge inward. Repeat for your fourth quadrant.

Step 5: Invert the plates and incubate your plate at 37 C for 24-48 hours.

Partial preview of the text

Download Using Streak Plate Technique to Isolate Single Colonies and more Study notes Microbiology in PDF only on Docsity!

Name ________________________ Per_

Using Streak Plate Technique to Isolate Single Colonies

OVERVIEW

Most microbiological work requires that a culture be started form a single colony. A colony is a single

bacterium that has multiplied on a solid medium into millions of clones of itself and looks like a round visible dot

on the solid medium. The streak plate method allows isolation of a single colony from a bacterial culture by

splitting the plates into quadrants and diluting the bacteria repeatedly as the loop is streaked through each

quadrant. Individual colonies of bacteria are referred to as colony forming units (CFUs), and these indicate a

mass of individual cells of same organism, growing together. However, it is important to remember that CFU is

not a measure for individual cells or spores as a colony may be formed from a single or a mass of cells or

spores.

OBJECTIVE

Isolate single colonies on a LB agar plate from a lawn of bacteria.

PROCEDURE

Step 1 : Obtain the proper media plate for your bacterial sample, such as an LB agar plate; label the bottom

with your name, date and bacterial species, and set up your materials in a sterile environment such as a clean

bench top.

Step 2 : Aseptically transfer a very small amount of your sample to the edge of your agar plate. Deposit your

sample (gathered with a sterile loop from the other agar plate) on the outer edge of the new agar plate. Use

your sterile loop to gently spread out the sample in a zig-zag manner along one quadrant of the plate from the

edge inward. Do not break the surface of the agar!

Step 3 : Rotate the plate 45 degrees, and drag the loop gently through your first quadrant (only once).

Continue to streak the second quadrant of your plate in a similar zig-zag manner from the outer edge of the

plate inward.

Step 4 : Rotate the plate 45 degrees, and drag the loop through the second quadrant once. Zig-zag streak the

third quadrant of your plate from the edge inward. Repeat for your fourth quadrant.

Step 5 : Invert the plates and incubate your plate at 37 C for 24-48 hours.

streak on the fourth plate (Figure 1-18). Properly

- FIGURE 1-ISa Beginning the Streak Pattern Streak the mixed culture back and forth in one quadrant of the agar plate. Use the lid as a shield and do not cut the agar with the loop. Flame the loop, then proceed. - FIGURE 1-ISb Streak Again Rotate the plate nearly 90 ° and touch the agar in an uninoculated region to cool the loop. Streak again using the same wrist motion. Flame the loop.

of getting isolation.

- FIGURE 1-ISc StreakYetAgain Rotate the plate nearly 9 0° and streak again using the same wrist motion. Be sure to cool the loop prior to streaking. Flame again. I - FIGURE 1-ISd Streak Into the Center After cooling the loop, streak one last time into the center of the plate. Flame the loop and incubate the plate in an inverted position for the assigned time at the appropriate temperature. I

LAB FOCUS QUESTIONS

Why do researchers incubate microorganisms at 37 C?
Why is important to invert the plates when incubating at 37 C?
Why is important to drag the inoculation loop through a previous quadrant when streaking to a new quadrant?
What does a colony forming unit (CFU) represent?
If 60 colonies formed on a LB agar plate, how many bacteria were plated? How many CFU are there?

Using Streak Plate Technique to Isolate Single Colonies, Study notes of Microbiology

Related documents

Partial preview of the text

Download Using Streak Plate Technique to Isolate Single Colonies and more Study notes Microbiology in PDF only on Docsity!

Name ______________________________________ Per_______________

Using Streak Plate Technique to Isolate Single Colonies

OVERVIEW

Most microbiological work requires that a culture be started form a single colony. A colony is a single

bacterium that has multiplied on a solid medium into millions of clones of itself and looks like a round visible dot

on the solid medium. The streak plate method allows isolation of a single colony from a bacterial culture by

splitting the plates into quadrants and diluting the bacteria repeatedly as the loop is streaked through each

quadrant. Individual colonies of bacteria are referred to as colony forming units (CFUs), and these indicate a

mass of individual cells of same organism, growing together. However, it is important to remember that CFU is

not a measure for individual cells or spores as a colony may be formed from a single or a mass of cells or

spores.

OBJECTIVE

Isolate single colonies on a LB agar plate from a lawn of bacteria.

PROCEDURE

Step 1 : Obtain the proper media plate for your bacterial sample, such as an LB agar plate; label the bottom

with your name, date and bacterial species, and set up your materials in a sterile environment such as a clean

bench top.

Step 2 : Aseptically transfer a very small amount of your sample to the edge of your agar plate. Deposit your

sample (gathered with a sterile loop from the other agar plate) on the outer edge of the new agar plate. Use

your sterile loop to gently spread out the sample in a zig-zag manner along one quadrant of the plate from the

edge inward. Do not break the surface of the agar!

Step 3 : Rotate the plate 45 degrees, and drag the loop gently through your first quadrant (only once).

Continue to streak the second quadrant of your plate in a similar zig-zag manner from the outer edge of the

plate inward.

Step 4 : Rotate the plate 45 degrees, and drag the loop through the second quadrant once. Zig-zag streak the

third quadrant of your plate from the edge inward. Repeat for your fourth quadrant.

Step 5 : Invert the plates and incubate your plate at 37 C for 24-48 hours.

streak on the fourth plate (Figure 1-18). Properly

of getting isolation.

Name ________________________ Per_