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Streak Plate Technique for Isolating Bacteria
Streaking to Obtain Pure Bacterial Cultures from Clinical Specimen
The purpose of streak plating is to spread out a clinical sample on solid growth media, so that individual, isolated bacterial colonies will grow.
Article Summary: Streaking a clinical sample onto a media plate is how specific bacteria are isolated so that the causative agent of a bacterial disease can be identified.
Streak Plate Technique for Isolating Bacteria
Two different styles of streak plate technique on Blood Agar.
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What Is a Bacterial Colony?
A colony is a visible spot on the surface of growing medium that containscontains millions of bacteria that, through cell division, arose from a single parent bacterium. This means that all bacteria in a colony are of the same species.
How to Isolate Bacteria Using Streak Plate Method
By using streak plate technique to spread a clinical sample out on the surface of a solid growth medium individual types of bacteria can be isolated. Here is the basic technique. See the instructional photo that appears with this article.
Supplies needed for streak plating:
- Petri dish of sterile TSY medium (or a specialized growing medium)
- Inoculation loop to transfer bacteria
- Bunsen burner or microincinerator to sterilize loop
- Clinical sample (sample obtained from person)
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SCIENCE PHOTOS
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Page last updated: 11/2015
What Is Bacterial Growth Media?
Asolid bacterial growth medium is a gel-like surface made from agar (a seaweed derivative), with an appearance similar to Jell-O. In addition to agar, growing media also contain water, nutrients and buffer to help the bacteria grow. Growth media are made to be sterile until inoculated with a bacterial sample.
Printable Step-by-Step
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Streak plate technique:
- Streak swab of clinical sample over one quarter of the sterile Petri dish in a back-and-forth "tornado" pattern. This is quadrant #1.
- Discard swab in biohazard bag.
- Sterilize loop in flame of Bunsen burner or hub of microincinerator.
- Allow loop to cool without waving it about.
- Place loop on next quadrant of Petri dish, next to quadrant #1. Gently drag the loop into quadrant #1 a few times, to obtain just a bit of bacteria from that first sample, then spread that material over quadrant #2, in another tornado pattern.
- Again sterilize loop in flame of Bunsen burner or hub of microincinerator, and allow loop to cool.
- Place loop in next quadrant of Petri dish, adjacent to quadrant #2. Gently drag the loop into quadrant #2 a few times, to obtain just a bit of bacteria from that sample, then spread that material over quadrant #3 in a tornado pattern.
