What is the significance of a "D-value" related to steam sterilization?

The D-value, or decimal reduction time, in steam sterilization represents the time required at a specific temperature to reduce the population of a particular microorganism by 90%, or one log10 unit. In other words, it's the time needed to kill 90% of the target microorganisms under defined conditions. The D-value is specific to the microorganism, the sterilization temperature, and the environmental conditions. It is a crucial parameter for determining the appropriate sterilization time required to achieve a desired level of sterility assurance. A lower D-value indicates that the microorganism is more susceptible to the sterilization process, while a higher D-value indicates greater resistance. Understanding the D-value of the target microorganism, typically Bacillus stearothermophilus for steam sterilization, is essential for calculating the sterilization time needed to achieve a specific sterility assurance level (SAL), such as 10^-6, meaning a one in a million chance of a non-sterile item.