In autoclaving (moist heat sterilization), the standard cycle of 121°C for 15 minutes at 15 psi (103 kPa) achieves a sterility assurance level of 10⁻⁶. The mechanism of sterilization is primarily through:
- A Oxidation of microbial proteins by steam-derived reactive oxygen species at high pressure
- B Disruption of lipid bilayer membranes at 121°C causing irreversible membrane lysis without protein damage
- C Hydrolysis of covalent bonds in proteins and nucleic acids due to presence of water at elevated temperature, coagulating proteins and destroying nucleic acids more efficiently than dry heat ✓
- D Generation of superheated steam above 150°C at 15 psi causing pyrolysis of microbial cell walls
Explanation
Autoclaving (moist heat) kills microorganisms — including bacterial endospores — primarily through hydrolysis of chemical bonds in macromolecules when water is present at high temperature. At 121°C, water molecules penetrate microbial cells and hydrolyse hydrogen bonds in proteins (causing denaturation and coagulation) and phosphodiester bonds in nucleic acids, far more efficiently than dry heat at the same temperature. The presence of water lowers the activation energy for these hydrolytic reactions. Dry heat (160°C/2 hours) acts through oxidation. Steam does not generate significant ROS. The process does not involve lipid pyrolysis; steam temperature at 121°C/15 psi is not superheated above 150°C.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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