Lethal Effects of Temperature (Exercise 48) Flashcards
What do elevated temperatures do to most microorganisms?
Elevated temperatures cause macromolecules (proteins) to denature and unfold, resulting in a loss of tertiary structure and biological activity. DNA and RNA structure is also affected.
Thermal Death Point
The lowest temperature at which a population of a target organism is killed in 10 minutes.
Thermal Death Time
The shortest time required to kill a population of microorganisms at a defined temperature.
Why is it important to inoculate a control plate for this experiment?
Inoculation of the control plate provides a point of comparison to the experimental plates, it ensures the bacteria were viable.
To measure the culture temperature, why is the thermometer placed in a tube separate from the culture?
If the thermometer were in the culture tubes, transfer would be difficult and contamination more likely (there is no cap on the tube).
Bacillus megaterium has a high thermal death point and long thermal death time, but it is not classified as a thermophile. Explain.
B. megaterium produces an endospore allowing survival, classification is based on the vegetative state.
Give three reasons why endospores are much more resistant to heat than are vegetative cells.
1) Endospores have a much lower water content, proteins are less likely to denature.
2) Calcium dipicolinate prevents denaturation due to heat
3) Proteins found in an endospore prevent denaturation of the nucleic acids.
List four diseases caused by spore-forming bacteria.
Botulism (Clostridium botulinum)
Gas Gangrene–food poisoning (Clostridium perfringens)
Anthrax (Bacillus anthracus)
Tetnus (Clostridium tetani)
Would heating the culture in a sealed, small-diameter tube that is totally immersed in a water bath produce more accurate results than the use of tubes that are partially submerged in a water bath?
Yes, tubes partially submerged allows for more temperature variation (uneven heating), sealed immersed tubes would yielld more accurate results.
