by Nicole Gadda
Fun Rating: 3/5
Difficulty Rating: 1/5
Isolation streaking gets a 1 out of 5 on the difficulty rating, which means this technique is beginner friendly and super easy!
What is the general purpose? Streaking is a technique used to isolate microorganisms (which are organisms like bacteria, fungi, and viruses that are too small to be seen by the naked eye) from a mixed population or to obtain isolated colonies for experiments.
Why do we use it? Isolation streaking is the foundation of microbiological techniques, allowing microbiologists to obtain single colonies for experiments. Microbiologists are scientists that study microbes like bacteria, fungi, and viruses. A “colony” is a group of microorganisms that originates from a single mother cell. This method allows microbiologists to run experiments with a uniform population. Furthermore, medical professionals use isolation streaking to isolate bacterial pathogens causing infectious disease. Once isolated, additional biochemical tests are used to identify the pathogen. Medical professionals do this by taking a sample from a patient suspected to have a bacterial infection. Then, they streak to isolate all the different microorganisms in the sample. Finally, they can run additional biochemical tests to identify the pathogen causing the infection.
How does it work? Streaking feels similar to painting! To start your bacterial Van Gogh, you will need an agar plate. Agar is a substance made from algae that is used for culturing (growing) bacteria, fungi, and other microorganisms. The agar plate is divided into four sections, and the sample is streaked, or “painted,” across the sections in a way that “thins out” the bacteria. In the first section, the sample is spread around with an inoculation loop. The loop is then sterilized using a Bunsen burner.
The heat from the flame kills any bacteria left on the loop, but the loop must cool down before it can be used on the next section, or there’s a risk of killing the bacteria on the plate. Once cool, the loop is used to drag some bacteria from the first section into the second section. The loop is sterilized again, and the bacteria that is in the second section is now streaked, or “painted,” across the next section. This process repeats until all four sections have been streaked. Finally, the plate is incubated at 37 degrees Celsius overnight. The next day, your “painting” will be complete and bacterial growth will be present! Growth will be heaviest in the first and second sections and lightest in the third and fourth sections, with single colonies present. These single colonies can then be used for medical purposes or microbiology experiments.
