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General Information About the Heat Tolerance Test
General Information About the Heat Tolerance Test
Different organisms thrive at different temperatures. Some bacteria and fungi, known as thermophiles, grow at temperatures high enough to kill other organisms. Psychrophiles, on the other hand, do best at low temperatures.
Boiling kills most but not all bacteria. Some bacteria form endospores, which can survive boiling. Autoclaving, however, adds high pressure to high heat and can inactivate spores.
In the heat tolerance experiment, you will demonstrate both the range of temperatures at which bacteria will grow as well as the effects of autoclaving and boiling on a species of bacteria that forms endospores.
The experimental protocol is here.
Reading the Results
Reading the Results
Heat Tolerance Part 1, Temperature Range
Heat Tolerance Part 1, Temperature Range
When incubated at 24°C, both Pseudomonas fluorescens and Escherichia coli grow. Note thatP. fluorescens does not grow at either 37°C or 56°C. What kind of organism do you think it is?--
When incubated at 37°C, only Escherichia coli grows.
When incubated at 56°C, only Geobacillus stearothermophilus grows. What kind of organism do you think G. stearothermophilus is? Does the name give you a clue?
Heat Tolerance Part 2, Heat Exposure
Heat Tolerance Part 2, Heat Exposure
The Bacillus subtilis in the top streak was neither boiled nor autoclaved. The Bacillus subtilis in the bottom right streak was boiled for 10 minutes, and the Bacillus subtilis in the bottom left streak (no growth) was autoclaved. Why did the boiled Bacillus subtilis grow? Would you expect Staphylococcus aureus or Escherichia coli to grow after being boiled for 10 minutes?
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