3.3: Pour and Spin Plate Method of Isolation

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Another method of separating bacteria is the pour plate method. With the pour plate method, the bacteria are mixed with melted agar until evenly distributed and separated throughout the liquid. The melted agar is then poured into an empty plate and allowed to solidify. After incubation, discrete bacterial colonies can then be found growing both on the agar and in the agar.

The spin plate method involves diluting the bacterial sample in tubes of sterile water, saline, or broth. Small samples of the diluted bacteria are then pipetted onto the surface of agar plates. A sterile, bent-glass rod is then used to spread the bacteria evenly over the entire agar surface (see Fig. \(\PageIndex{1}\)) in order to see isolated colonies (see Fig. \(\PageIndex{2}\)). In Lab 4 we will use this technique as part of the plate count method of enumerating bacteria.

Fig. \(\PageIndex{1}\): Using a Bent Glass Rod and a Turntable to Spread a Bacterial Sample	Fig. \(\PageIndex{2}\):Single Colonies from the Spin-Plate Method

Streak the inoculum over area "1" as shown above. Then flame the loop and cool it by sticking it into the edge of the agar. Rotate the plate 90 degrees counterclockwise.	Rotate the plate so area "1" is on your left. Drag your stetile inoculating loop through area "1" two times and spread out over area "2" as shown above. Then flame the loop and cool it by sticking it into the edge of the agar. Rotate the plate 90 degrees counterclockwise.
(Copyright; Gary E. Kaiser, Ph.D. The Community College of Baltimore County, Catonsville Campus CC-BY-3.0)

Contributors and Attributions

Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)