Streak Plating

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Streak Plating

  1. 1. Streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a culture can be grown on a new plate so that the organism can be identified, studied, or tested.
  2. 2. PURPOSE • The purpose of making a streak plate is to isolate a single colony of bacteria on an agar filled petri dish. • You may need to culture this colony for a later experiment. • A colony is created after a single bacteria divides many times creating a mass of genetically identical bacteria. • When performing this procedure keep in mind that you want to dilute a small sample to a point where 1 portion of a petri dish has just 1 bacteria.
  3. 3. MATERIALS Wire loop Petri dish
  4. 4. PROCEDURES To cool the sterilized loop, touch it to a sterile agar plate, then dip the loop into a sample containing a mixture of bacteria to pick them up.
  5. 5. Before continuing to streak the plate, the remaining bacteria on the loop are first killed in the flame, after cooling the sterilized loop, drag it through the previous path, picking up a small number of bacteria and spreading them into a new area of the plate.
  6. 6. After sterilizing and cooling the loop again, the procedure is repeated. With each new path, the loop picks up a smaller number of bacteria, and therefore can spread them farther and farther apart.
  7. 7. During incubation, the bacteria multiply and produce colonies. Each colony consists of millions of cells derived from a single parent bacterium. The isolated colonies found in the last streak represent isolated strains to ensure the strains purity, the streak plate procedure is usually repeated a few more times, using an isolated colony as the source of starting bacteria.

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