Definition of Sterilization

Sterilization is a broad term that refers to any process that removes or kills all forms of microorganisms. This includes bacteria, fungi, viruses and protozoans including their spore forms which are usually very resistant. This refers to life forms that are on the surface, within a fluid, medications, or compounds such as buffers and culture media. Proper sterilization is easily achieved with combinations of heat, high pressure, filtration, chemicals and irradiation.

More recently, sterilization has evolved to disable infectious proteins such as prions to some degree depending on the molecular form it is in. Different animals carry different molecular forms. Prions are abnormally folded proteins that are associated with Transmissible Spongiform Encephalopathies (TSE). For prion destruction, it is suggested that you autoclave at 250-270 °F (121-132 °C) for 60 minutes at 15 psi (pounds per square inch) or 143 °C for a minimum of 18 minutes (15 psi). This has been demonstrated to work on the prion disease known as scrapie (TSE, strain 263K). This prion affects goats and sheep. However, Creutzfeldt-Jacob’s Disease (CJD, human disease) and Bovine Spongiform Encephalitis (BSE, cow disease) are considerably more resistant. What needs to be done is to break the protein’s peptide bonds essentially fragmenting the protein into tiny polypeptide pieces.

Bovine Spongiform Encephalitis positive brain tissue has been heated to 273-280 °F (134-138 °C) for 18 minutes and injected into mice. Much of the prion activity remained. If you suspect that you have prion contamination or know that you do, make sure you wash the item(s) well before autoclaving. In fact, that’s true of all things you will autoclave. Washing and proper rinsing are important steps of the sterilization process. This eliminates large aggregates that would prevent steam from penetrating. This is not unlike sweeping a floor before you wash it. 

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