Figure 1: Rate of microbial inactivation on exposure to sterilization processes. In this case, the test microorganism (generally bacterial spores) at a starting population of 106 CFU (colony forming units) is exposed to the sterilizing agent under two conditions (A and B). The number of microorganisms can be determined over contact time using a direct-enumeration method. In process A, “tailing” is observed, which may not allow the extrapolation of the kill curve to a defined probability of survival (known as an SAL, sterility assurance level). In process B, the kill curve is linear, allowing extrapolation (dotted line) to an SAL of 10-6.