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Biology LibreTexts

7.3: Results

  • Page ID
    15994
  • A. The Autoclave

    Describe and draw the results of the autoclave experiment.

    What can you conclude about the effectiveness of the autoclave as an instrument for sterilization?

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    B. Effect of Temperature

    For each incubation temperature, record growth pattern as follows:

    0 no growth

    + light growth

    ++ medium growth

    +++ heavy growth

    Week 2 Results

    Bacterial species 4˚C Room temperature 37˚ C 55˚ C
    Micrococcus roseus
    Escherichia coli
    Geobacillus stearothermophilus
    Serratia marcescens

    Based on these results, how would you classify:

    Micrococcus roseus ____________________________________

    Escherichia coli ____________________________________

    Geobacillus stearothermophilus ____________________________________

    Serratia marcescens ____________________________________

    Do you notice any differences in the appearance of the growth of Serratia at different temperatures? If so, describe what you observe.

    Your instructor will again collect the plates that had been incubated at 4˚C and incubate them for another week at 4 ˚C, room temperature, 37˚C and 55˚C (one plate at each temperature).

    Week 3: Record the results for plates that were initially incubated at 4˚C and then placed in warmer temperatures.

    Bacterial species Initial incubation temperature (week 1) Week 2: Room temperature Week 2: 37˚C Week 2: 55˚C
    Micrococcus roseus 4˚C
    Escherichia coli 4˚C
    Geobacillus stearothermophilus 4˚C
    Serratia marcescens 4˚C

    Based on these results, what can you conclude about the effect of cold temperatures on these organisms?

    C. Effect of Moisture

    Week 2: describe any changes in appearance of the tubes.

    Week 3: Record + or – growth for each bacteria tested

    Bacteria Growth
    Staphylococcus aureus
    Proteus vulgaris
    Bacillus subtilis
    Mycobacterium phlei

    Based on these results, which bacteria can survive drying conditions?

    Can you think of any reasons why these species would be able to survive in a dry environment?

    D. Demo: Determination of the TDT

    Observe the plates at the instructor’s table, and record the growth of the bacteria at each incubation time in the table below. Record growth as 0, +, ++, or +++.

    Temperature 65˚C 65˚C 65˚C 65˚C 80˚C 80˚C 80˚C 80˚C
    Incubation Time (min.) 0 15 20 30 0 15 20 30
    Escherichia coli
    Micrococcus roseus
    Staphylococcus aureus
    Geobacillus stearothermophilus

    Based on the information in the data table, determine the TDT for each organism at the given temperature.

    Bacterial Species 65˚C 80˚C
    Escherichia coli
    Micrococcus roseus
    Staphylococcus aureus
    Geobacillus stearothermophilus

    E. Effect of UV Radiation

    Record the results for each plate as follows:

    0 no growth

    + light growth

    ++ medium growth

    +++ heavy growth

    Also note any differences in appearance of growth on each of the plates.

    Bacteria Visible light UV lid on UV lid off 5 sec UV lid off 10 sec UV lid off 1 min UV lid off 10 min
    Serratia marcescens
    Bacillus subtilis

    Based on these results, answer the following questions:

    1. Did visible light have any effect on microbial growth? ________________________________________

    2. Did UV exposure with the lid on have any effect on microbial growth?___________________________

    3. Explain any differences you observe between the two species tested. __________________________________________________________________

    4. Describe any other differences in the appearance of colonies on the irradiated plates. _______________________________________________________________________