During heat sterilization in an autoclave, the D-value (decimal reduction time) concept is used to validate sterilization efficacy. The standard autoclaving cycle is 121°C for 15 minutes at 15 psi pressure. Which organism is used as the biological indicator (BI) to validate autoclave performance?
- A Bacillus cereus spores (ATCC 11778)
- B Clostridium sporogenes spores (ATCC 7955)
- C Geobacillus stearothermophilus spores (formerly B. stearothermophilus) ✓
- D Bacillus subtilis var. niger spores
Explanation
Geobacillus stearothermophilus (formerly Bacillus stearothermophilus) spores are the biological indicator for moist heat (autoclave) sterilization because they are highly resistant to moist heat with a D121 value of ~1.5 minutes; commercial strips contain 10^6 spores. After autoclaving, the strips are incubated at 56°C — no growth (no color change in medium) confirms successful sterilization. Bacillus subtilis var. niger (globigii) spores are used for dry heat (160°C hot air oven) and ethylene oxide gas sterilization validation. C. sporogenes ATCC 7955 is used for steam-in-place validation at lower temperatures.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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