A Method of Increasing Test Range and Accuracy of Bioindicators: Geobacillus stearothermophilus Spores

Abstract

Spores of Geobacillus stearothermophilus are very sensitive to changes in temperature. When validating sterilizing processes, the most common bioindicator (BI) is spores of Geobacillus stearothermophilus ATCC12980 and ATCC7953 with about 10⁶ spores /BI and a D₁₂₁-value of about 2 minutes in water. Because these spores of Geobacillus stearothermophilus do not survive at a F₀-value above 12 minutes, it has not been possible to evaluate the agreement between the biological F-value (F_BIO) and physical measurements (time and temperature) when the physical F₀-value exceeds that limit.

However, it has been proven that glycerin substantially increases the heat resistance of the spores, and it is possible to utilize that property when manufacturing BIs suitable to use in processes with longer sterilization time or high temperature (above 121°C). By the method described, it is possible to make use of the sensitivity and durability of Geobacillus stearothermophilus' spores when glycerin has increased both test range and accuracy.

Experience from years of development and validation work with the use of the highly sensitive glycerin-water-sporesuspension sensor (GWS-sensor) is reported. Validation of the steam sterilization process at high temperature has been possible with the use of GWS-sensors. It has also been shown that the spores in suspension keep their characteristics for a period of 19 months when stored cold (8°C).