Streak Plating Technique Tutorial
There are many methods of isolating bacterial colonies. Three of the most commonly used are the following: spread plating, pour plating and of course, streak plating. In this tutorial, you will be learning more about streak plating. I have provided a comprehensive and useful resources for you to get back to when you need them.
The Streak Plating
This method is conducted with the objective of obtaining one isolated bacterial colony in mind. Isolating a colony is crucial in the identifying the strain of bacteria that grows on your plate. By using this method, you will get surface aerobic bacterial colonies (measured as CFU or Colony Forming Units).
The equipment/materials needed are as follows:
- Nutrient Agar, melted then hardened in a petri dish
- Inoculating loop
- Lamp or Bunsen burner
- A sterile and clean environment
Compared to the other methods (pour plate and spread plate), streak plating do not need a definite amount of bacteria to start with. Usually, when streaking plates, the amount needed is only a loop-full of bacteria from one isolated colony.
So you are probably wondering how we got here. Before you begin, make sure that the area where you will conduct your experiment is clean (using 70% ethanol), the Bunsen burner is turned on (important for air conduction), and the other materials are in place. I shall enumerate the crucial steps below.
Mark and divide the bottom of the petri dish into four quadrants. Marking it is not compulsory. Just imagine your plate being divided into these four quadrants and that would suffice.
Flame the inoculating loop until it turns red. This will ensure that most of the bacteria on it would be killed and this would help minimize the risk of contamination. Let the loop cool down for a few seconds. Another way to cool it down is to touch the agar medium (near the edge of the petri dish) for one second before taking the selected bacterial colony.
Take one isolated colony and streak it over the first quadrant of the new plate using closed parallel streaks.
A point to take note of is that when you open the petri dish lid, do not fully open it. By leaving just enough opening for you to streak, it would reduce the risk of contamination.
After streaking the first quadrant, flame the loop until it turns red. Rotate the plate 90 degrees and start streaking the second quadrant.
Repeat the flaming-rotating-streaking step two more times for the other quadrants.
Here is an illustration that shows the steps of streak plate method.
Here is a compilation of important credible websites that will definitely help you understand more about the topic. These are fantastic sites from various universities and colleges and it is advisable to scan through some of them.
- Streaking and Inoculating Plates. Boston University.
- Streaking Microbial Cultures on Agar Plates. University of Missouri--St. Louis.
- Streak Plate method Simulation. University of Michigan.
- Streak Patterns. University of Wisconsin-Madison.
- Simple Staining and Streaking. Washington State University.
- Strategies for Obtaining Pure Isolates. Rice University.
- Procedure for Streaking a Plate for Isolation. Western Michigan University.
- Plate Streaking and Growth. University of Texas.
- Streaking for Isolation. Clark University.
- Streak Plate Activity. Maricopa Community College.
- Single Colony Isolation. College of Lake County.
- Streaking Plates for Isolation. Hawaii University.
- Pure Culture Techniques. San Diego Miramar College.
- Streak Plate Method (from page 8). University of Idaho.
Practice makes perfect. Click on the video below to see what kind of practice you need in order to perfect that perfect wiggle/streak.
A very comprehensive video that shows the streaking technique, do's and don'ts, and the materials needed for the experiment.
Similar streaking technique on blood agar.
Another useful video that shows the streaking technique with visible pen-marked quadrants on the plate.
Amrita University video that shows the streaking technique from a liquid broth medium on to the agar plate.