Nerdy Science Blog

Why do plate streaking? A friend of mine asked.

Why? Because this is one of the best, cheap, easiest ways to isolate a pure culture. And plate streaking can be fun when it come to coloring~

Although this is easy and cheap, it doesn’t mean it is not important. How pure is your culture often determine “dead or alive” of your microbiological experiment; and by mastering this simple technique, it can save your day…

Metallic green E. coli on EMB agar, picture derived from my undergrad thesis.

E. coli give a metallic green color on EMB (Eosin methylene blue) agar, I was soooo fascinated by the mysterious, lovely, shining color which later become one of my favourite.

There are ways of streaking techniques, the method which I demonstrated above is called Three Quadrant Streaking, one of the famous methods. However, for the methods, the materials remain the same.

Materials:

Wire loop
Bunsen burner
Agar (normally use nutrient agar/LB agar)
Culture, perhaps mixed.

Methods:

[source]

The streaking sequence is the one I used before.

1. Flame the wire loop until red-hot, cool down. Loop will usually fully cool down 15~20 seconds.
2. Touch the sterile loop with the mix culture, streak like diagram 1.
3. Repeat step number 1, follow diagram 2.
4. Repeat step number 1, follow diagram 3.
5. After final streaking, flame the wire loop until red-hot again before put on bench.

*note: Avoid touching first streaking too many time during 2nd streak, 1~2 overlapping is sufficient, otherwise it might cause the streaking too confluent with bacteria culture and might resulting failure in isolating single colony. Same concept apply to 3rd streak.

As I said, there are ways to perform this easy task. Both of the picture below are Four Quadrant Streaking which I found online.

[source]

another type of four quadrant streaking [source].

To make things fun, you can have more pattern. The principle behind the art of streaking remain the same.

[source]

Happy Streaking~!

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