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?
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. _______________________________________________________________________