HeatLabOL.docx

BIO2073- Microbiology lab

Summer Quarter 2020

Lab Report: Heat as a method of control

1. What was the objective of this lab exercise?

2. Use the following table to document your data. For each plate that you look at, be sure to indicate the species, and the temperature used. Then, for each time point, evaluate the relative amount of growth in each section using a scale from 0-4 where
0 = No growth 4= heaviest growth

Organism

63°C

72°C

0 sec

30 sec

1 min

2 mins

5 mins

15mins

0 sec

30 sec

1 min

2 mins

15 mins

3. Why was it important to plate out a sample at 0 seconds, prior to exposing the culture to heat?

4. In general, was 63°C or 72°C more effective at killing the microbes? Does this align with the results you expected? Why or why not?

4. Both “young” (less than 24 hours) and “old” (several weeks) cultures of B. subtilis were used in this experiment. Why do you think this was done? Hint: what do you know about the Bacillus genus and their survival mechanisms? Why use Bacillus and not old/young E.coli for example?

6. The thermal death time and the term death point are two different ways to describe a microbe’s sensitivity to heat. Which of these two measurements were we evaluating in this experiment? Explain your answer.
7. Give an example of a non-laboratory use of each of the following methods to control microbial growth:
a. Incineration:
b. Pasteurization:
c. Autoclaving:

Bonus! The species Geobacillus stearothermophilus is often used as an indicator species to test the effectiveness of autoclaving. Why do you think this species is used instead of E. coli or B. subtilis?