Microbiology - 004 - Spread Plate Method

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The spread plate method is a technique to plate a liquid sample containing bacteria so that the bacteria are easy to count and isolate. A successful spread plate will have a countable number of isolated bacterial colonies evenly distributed on the plate. 

The spread plate method uses a tool called a plate spreader (or hockey stick). To sterilize a plate spreader, first douse it in ethanol. Then, pass it briefly through the flame of a Bunsen burner and carefully allow the ethanol to burn off. The goal is only to burn off the ethanol; do not hold the plate spreader in the flame. Hold the plate spreader away from the ethanol canister and allow all of the alcohol to burn off, taking care not to let flaming ethanol drop onto the bench top. 

Using a pipette, transfer a measured volume from a liquid sample containing bacteria and dispense it onto a fresh plate. Immediately move on to spreading the liquid; do not let it sit on the plate while you dispense other samples. 
Sterilize a plate spreader and touch it to the surface of the agar, away from the dispensed liquid, to cool. To spread the dispensed liquid around the plate, gently push the plate spreader back and forth. Use your other hand to hold the lid above the plate and to spin the plate to get an even spread. Continue to spread until the liquid has formed an even layer on the surface of the media. Replace the lid. 

The spread plate is ready to incubate. If your spread plate was successful, after incubation you should have isolated, countable colonies evenly spread across the surface of the plate.

The spread plate method is a technique to plate a liquid sample containing bacteria so that the bacteria are easy to count and isolate. A successful spread plate will have a countable number of isolated bacterial colonies evenly distributed on the plate. 

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