A widely used method for heat sterilization is the autoclave, sometimes called a converter or steam sterilizer. Autoclaves use steam heated to 121–134 °C (250–273 °F) under pressure. To achieve sterility, the article is placed in a chamber and heated by injected steam until the article reaches a temperature and time setpoint. Almost all the air is removed from the chamber, because air is undesired in the moist heat sterilization process (this is one trait that differs from a typical pressure cooker used for food cooking). The article is held at the temperature setpoint for a period of time which varies depending on what bioburden is present on the article being sterilized and its resistance (D-value) to steam sterilization. A general cycle would be anywhere between 3 and 15 minutes, (depending on the generated heat) at 121 °C (250 °F) at 100 kPa (15 psi), which is sufficient to provide a sterility assurance level of 10−4 for a product with a bioburden of 106 and a D-value of 2.0 minutes. Following sterilization, liquids in a pressurized autoclave must be cooled slowly to avoid boiling over when the pressure is released. This may be achieved by gradually depressurizing the sterilization chamber and allowing liquids to evaporate under a negative pressure, while cooling the contents.
Proper autoclave treatment will inactivate all resistant bacterial spores in addition to fungi, bacteria, and viruses, but is not expected to eliminate all prions, which vary in their resistance. For prion elimination, various recommendations state 121–132 °C (250–270 °F) for 60 minutes or 134 °C (273 °F) for at least 18 minutes. The 263K scrapie prion is inactivated relatively quickly by such sterilization procedures; however, other strains of scrapie, and strains of Creutzfeldt-Jakob disease (CKD) and bovine spongiform encephalopathy (BSE) are more resistant. Using mice as test animals, one experiment showed that heating BSE positive brain tissue at 134–138 °C (273–280 °F) for 18 minutes resulted in only a 2.5 log decrease in prion infectivity.
The statistical discussion of "sterility assurance level" and "bioburden" already seems to preclude any possibility of absolute certainty, such as "...all resistant bacterial spores..."
Question: The research cited in Is it known how some heat-resistance Bacillus spores repair their DNA after having been heated to 420 °C? (see below) shows an abrupt transition between 420 and 430 °C. Can we therefore assume that the sentence "Proper autoclave treatment will inactivate all resistant bacterial spores..." is just plain wrong If so, just how widespread are autoclave-resistant bacterial spores?
Related: Why do we use an autoclave at 121°C (250F)? (Origin)
The 2018 Extremophiles paper: Beladjal, L., Gheysens, T., Clegg, J.S. et al. Life from the ashes: survival of dry bacterial spores after very high temperature exposure. Extremophiles 22, 751–759 (2018). https://doi.org/10.1007/s00792-018-1035-6 (also downloadable from researchgate).