AIIMS November 2011 – MCQ 155

Which of the following is used to test the efficiency of sterilization in an autoclave?
A. Clostridium tetani
B. Bacillus stearothermophilus
C. Bacillus pumilus
D. Bacillus subtilis

(Modified repeat question – AIIMS Nov 10 – AA q67)

Correct answer : B. Bacillus stearothermophilus

Biological Indicator Monitoring of autoclaves – Operators must use the biological indicator Bacillus stearothermophilus placed at the center of a load processed under standard operating conditions at least monthly to confirm the attainment of adequate sterilization conditions.

  • Use spore ampules or strips with an average population of 104 to 106 organisms adjusted to the following resistance data – survives steam heat at 250º F for five minutes and is killed at 250º F in thirteen minutes.
  • The most reliable means for determining whether a sterilizing cycle has been successful is by planting biological indicators throughout the load before the load is subjected to the sterilization process.
  • Operate the autoclave in accordance with manufacturer’s instruction. The cycle (time and temperature) shall be the minimum as required by user’s lab procedures.
  • Record chamber temperature as shown by the sterilizer indicator autoclave’s thermometer.
  • Upon completion of cycle, fast exhaust the chamber and remove test spore strips from the autoclave.
  • Incubate the Bacillus stearothermophilus test strips according to manufacturer’s instructions.
  • Record results on the Quality Control Checklist



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AIIMS November 2011 – MCQ 154

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