In monitoring the efficacy of autoclaving (134°C, 3 minutes), which biological indicator organism is used, and what principle does it employ?

• A Bacillus atrophaeus spores; used because they are resistant to ethylene oxide
• B Geobacillus stearothermophilus spores; these are the most heat-resistant spores known and must be killed for sterilization to be confirmed ✓
• C Clostridium sporogenes spores; anaerobic indicators for autoclaving
• D Aspergillus niger spores; used for monitoring dry heat ovens

Explanation

Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) spores are used as biological indicators for steam autoclaving (moist heat sterilization). They are the most thermoresistant organisms known; their D-value (decimal reduction time) at 121°C is 1.5–2.5 minutes. Complete killing of G. stearothermophilus spores (confirmed by no growth of spore strips in culture broth after autoclaving) validates sterilization efficacy. Bacillus atrophaeus spores are used for monitoring ethylene oxide (EtO) sterilization. Chemical indicators (Browne's tubes, autoclave tape) change colour but confirm temperature/time parameters — not biological killing.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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