Microbial control methods — A/L Biology

How do I practise Microbial control methods?

1 question with a worked solution

1. Which operating parameters are standardly prescribed for routine autoclaving to ensure total destruction of resistant bacterial endospores (such as Geobacillus stearothermophilus)?
   1. A) 72 °C for 15 seconds followed by rapid chilling
   2. B) 160 °C in a dry-air oven for 30 minutes
   3. C) 100 °C at atmospheric pressure for 10 minutes
   4. D) 121 °C at 15 psi (103 kPa) pure steam pressure for 15–20 minutes
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   Correct answer: D) 121 °C at 15 psi (103 kPa) pure steam pressure for 15–20 minutes

   Moist heat sterilization in an autoclave operates with saturated steam at 121 °C under 15 pounds per square inch (psi / 103 kPa) above atmospheric pressure for at least 15 to 20 minutes. This achieves complete denaturation of proteins and thermal coagulation of all vegetative cells, viruses, and endospores.

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   Step 1: Sterilization criteria: - Boiling (100 °C): kills vegetative cells but not resistant bacterial endospores. - Dry heat oven: 160-170 °C for 2 hours. - Pasteurization: 72 °C for 15 s (reduces pathogens, does not sterilize). - Autoclave standard: 121 °C at 15 psi steam for 15-20 min. Answer: 121 °C at 15 psi (103 kPa) pure steam pressure for 15–20 minutes.
   Modelled on: the A/L Biology examination pattern

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Where does Microbial control methods fit in the syllabus?

Year 2 · Term 3