Physical Methods of Microbial Control: Heat

Key Terms

• Thermal Death Point: The temperature required to kill all microbes in a sample in 10 minutes.
• Thermal Death Time: The time required to kill all microbes in a sample at a given temperature.
  • Importance: Thermal death time is considered a more useful metric for comparing microbial resistance.

Moist Heat vs. Dry Heat

• Moist Heat

  • More effective in microbial killing.
  • Example: Boiling.
    • Not suitable for laboratory use as some endospores can survive (e.g., Clostridium botulinum requires 116°C to kill).
    • Boiling is effective for home use (e.g., boiling water, baby bottles).

• Dry Heat

  • Requires higher temperature and longer time.
  • Example: Dry heat sterilization.
    • 170°C for 2 hours needed for effective sterilization.
  • Compared to moist heat:
    • Autoclave (moist heat): 121°C for 15 minutes.

Incineration

• Method: Destroys microbes by oxidation (burning electrons off).
• Laboratory Use: Flaming wire loops with a Bunsen burner or using incinerators.

Conclusion

• Moist heat is generally preferred due to its efficiency and effectiveness in microbial control.
• Future topics will cover autoclaves and pasteurization in detail.

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• Remember to handle laboratory equipment carefully to prevent accidents and ensure proper sterilization.