The laboratory hot air oven used for sterilising glassware and oily preparations is undergoing routine validation with a biological indicator. Which spore-forming organism is the accepted biological indicator for dry heat sterilization?
- A Geobacillus stearothermophilus
- B Clostridium sporogenes
- C Bacillus atrophaeus (formerly Bacillus subtilis var niger) ✓
- D Bacillus megaterium
Correct answer: C. Bacillus atrophaeus (formerly Bacillus subtilis var niger)
Explanation
Dry heat ovens are monitored with spores of Bacillus atrophaeus, known in older literature as Bacillus subtilis var niger, chosen for its marked resistance to desiccation and heat. The commonest error is selecting Geobacillus stearothermophilus: that organism is highly moist-heat resistant but relatively dry-heat susceptible, so it is the indicator for autoclaves, not hot air ovens. Standard dry heat cycles run at 160 degrees Celsius for 2 hours.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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