The biological indicator used to monitor the efficacy of moist heat (autoclave) sterilization is spores of:
- A Geobacillus stearothermophilus ✓
- B Bacillus atrophaeus (formerly B. subtilis var. niger)
- C Bacillus anthracis endospores
- D Clostridium sporogenes spores
Correct answer: A. Geobacillus stearothermophilus
Explanation
Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) spores are the standard biological indicator for autoclaving (121°C, 15 psi, 15 minutes). These thermophilic bacteria produce highly heat-resistant spores with a D121 value high enough to serve as a stringent test. Failure to kill these spores indicates inadequate sterilization. Bacillus atrophaeus (B. subtilis var. niger) spores are used for dry heat sterilization (160–170°C) and ethylene oxide sterilization. Clostridium sporogenes is not a standard indicator.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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