ABSTRACT
M ICROBIOLOGISTS are familiar with the concept that bacteria sub-jected to a sterilizing agent will, in theory, die exponentially with time at a uniform rate. A constant percentage of the microbial population is inactivated with each successive time interval. The absorbed dose required to destroy 90%, or one ( l ) log, of the microbial population is defined as the D,, value, or decimal reduction value. Therefore, a semi-log plot (Figure 9) will yield a straight-line relationship. Note that when the line crosses below 10°, resulting in less than one survivor, it is expressed as a probability of survival. Thus, the 1 0-6 survivor level or sterility assurance level (SAL) or a 12-spore log reduction (SLR) represents a one-in-one million probability of one microorganism surviving the process.
