Streak Plate Method of Isolation

One of the most important techniques you will learn this semester is how to streak for isolation. As you might guess, the purpose of streaking for isolation is to produce isolated colonies of an organism on an agar plate.  This is useful when you need to separate organisms in a mixed culture or when you need to study the colony morphology of an organism.

When streaking for isolation, you will begin by streaking a portion of your agar plate with an inoculum.  You will then streak successive areas of your plate in an attempt to dilute the original inoculum so that single colony forming units (CFUs) will give rise to isolated colonies.

For this exercise, you will need a spray bottle of 10% Lysol, paper towels, a Nutrient Agar plate, a Bunsen burner, a striker, an inoculation loop, and a stock culture from which to take the inoculum.  A Sharpie will also be helpful.

Using proper technique, flame your loop.

Insert your loop into the tube and remove some inoculum. You don't need a huge chunk.

Using the diagram on page 121 of your book (or a diagram provided to you by your instructor), streak the first section of your plate. Flame your loop again.

Touch the loop to an uninoculated section of the agar to cool it before using it to manipulate your organism. Using your diagram, streak the second section of the plate.

Flame your loop again, and again touch it to an uninoculated section of plate to cool it.  Use your diagram again, and streak your third quadrant.

Flame your loop again, cool it, and streak your final quadrant with the aid of your diagram.

Flame your loop once more.