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4.6: Results

  • Page ID
    123043
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    A. Plate Count

    1. Choose a plate that appears to have between 30 and 300 colonies.

    • Sample 1/100,000 dilution plate. (See Fig. \(\PageIndex{1A}\).)
    • Sample 1/1,000,000 dilution plate. (See Fig. \(\PageIndex{1B}\).)
    • Sample 1/10,000,000 dilution plate. (See Fig.\(\PageIndex{1C}\).)

    Fig. \(\PageIndex{1A}\): 1/100,000 Dilution of Bacterium (10- 5)

    Fig. Fig. \(\PageIndex{1B}\): 1/100,000 Dilution of Bacterium (10- 5)

    Fig. \(\PageIndex{1C}\): 1/10,000,000 Dilution of Bacterium (10- 7)

    Photograph showing colonies on a 1/100,000 dilution plate during the plate count procedure. Photograph showing colonies on a 1/1,000,000 dilution plate during the plate count procedure. Photograph showing colonies on a 1/10,000,000 dilution plate during the plate count procedure.
    This plate has over 300 colonies and cannot be used for counting. This plate has between 30 and 300 colonies and is a suitable plate for counting. This plate has less than 30 colonies and cannot be used for counting.
    (Copyright; Gary E. Kaiser, Ph.D. The Community College of Baltimore County, Catonsville Campus CC-BY-3.0)

    2. Count the exact number of colonies on that plate using the colony counter (as demonstrated by your instructor).

    3. Calculate the number of CFUs per ml of original sample as follows:

    The number of CFUs per ml of sample =

    The number of colonies (30-300 plate) X

    The dilution factor of the plate counted

    ____________ = Number of colonies

    ____________ = Dilution factor of plate counted

    ____________ = Number of CFUs per ml

    4. Record your results on the blackboard.

    B. Direct Microscopic Method

    Observe the demonstration of the Petroff-Hausser counting chamber.

    C. Turbidity

    Observe your instructor's demonstration of the spectrophotometer.

    Contributors and Attributions

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


    4.6: Results is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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