Survivor plots and sterility assurance levels
Start with the big picture
A survivor plot displays microbial survivors against exposure time or dose on a semi-log scale. A straight line indicates first-order death kinetics, while its slope helps describe the rate of kill. D-value expresses the exposure needed for a 1-log reduction; Z-value relates temperature change to a tenfold change in D-value, and F₀ represents equivalent lethality at 121 °C using a z-value of 10 °C. Sterility assurance level (SAL) describes the probability that a unit remains non-sterile after processing. The lesson connects these concepts to overkill and bioburden-based cycles, biological-indicator testing, and monitored process parameters. It also considers survivor-curve tailing as a signal that the cycle may need revision.
What you'll learn
- Interpret survivor plots and distinguish first-order death kinetics from tailing.
- Explain how D-value, Z-value, and F₀ describe sterilization lethality.
- Describe SAL and compare overkill with bioburden-based cycle approaches.
- Identify how biological indicators and process monitoring support cycle validation.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
