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Biology LibreTexts

10.1: Learning Objectives

  • Page ID
    40211
  • Learning Objectives

    After this lab you should be able to:

    1. Perform a serial dilution on a bacterial culture.
    2. Design a dilution scheme for a Standard Plate Count.
    3. Determine the final dilutions in a serial dilution and the # of CFU/ml (cell density) of the original sample.
    4. Utilize the Spectrophotometer to determine the OD of bacterial culture samples.
    5. Graph absorbance vs. the dilution of your serial dilutions.
    6. Compare and contrast Direct Count, Standard Plate Count, and the Indirect Turbidimetric method of enumeration bacterial counts in a sample.

    Why do we want to know how many bacteria are in a sample or specimen? Do you think it’s important to know the number of microbes in food? Quantifying the bacterial level in a sample can be done in several ways. New rapid diagnostic tests can help identify particular bacteria in a sample, but the total count is informative in a manufacturing or diagnostic process.

    What about in human disease? Typically, urinary tract infections are determined not by the mere presence of bacteria in a urine sample, but by the magnitude of bacteria (>105 CFU/ml) in the sample. 1, 2, 3

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