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Biology LibreTexts

9.3: Results

  • Page ID
    16008
  • A. The Microbiology of Milk

    Record the results of your experiment in the table below. Record growth as 0, +, ++, or +++. Describe any notable growth characteristics.

    TSA Plates

    Amount of Growth Growth Characteristics
    Regular pasteurized (refrigerated)
    Regular pasteurized (room temperature)
    UHT pasteurized (refrigerated)
    UHT pasteurized (room temperature)

    Which type of milk had the largest number of bacteria? ___________________________________

    Was your earlier prediction correct? ______________

    B. The Microbiology of Poultry

    Count the CFUs on your plates. Record your numbers in the table below. If there are too many CFUs to count, just write “TMTC” (too many to count). Remember—a countable plate that is considered statistically significant should have between 30 -300 CFUs.

    Record your plate counts below. Make note of any notable growth characteristics (e.g., fungal-like growth, colony colors, etc.) Note: not all of your plates may be in the countable plate range (they may have many more or many fewer colonies). You need only record the numbers for the countable plates.

    Based on the results for each countable dilution, determine the total number of bacteria in the original sample. Then average these numbers to obtain a more significant result.

    Dilution plated Amount spread on plate Growth characteristics Number of CFUs/plate Number of bacteria/ml in original sample (No. CFUs x Dilution factor x 10)
    Tube 2 =10-4 0.1 ml
    Tube 3 = 10-5 0.1 ml
    Tube 4 = 10-6 0.1 ml

    Average number of bacteria/ml in original sample:

    If you also did this experiment using EMB plates, would you expect more colonies on the TSA or the EMB plates? Explain your answer.

    What type of bacteria could you identify by using the EMB plates, and why would these bacteria be of concern for human health?

    Class Data

    For the results of the experiment to be more statistically significant, data from the entire class will be collected and written in the following table.

    Number of bacteria/ml in original sample
    Table 1
    Table 2
    Table 3
    Table 4
    Average

    C. Microbiology of Food

    Observe the plates of all of the food materials. Rate the food material based on the relative number of bacterial colonies seen on each plate:

    least bacteria ___________________ < _____________________ < ___________________ < __________________ most bacteria