Effect of Rubber Stopper Composition, Preservative Pretreatment and Rinse Water Temperature on the Moist Heat Resistance of Bacillus stearothermophilus ATCC 12980

Bacillus stearothermophilus spores (liquid suspension) were inoculated onto rubber stoppers and exposed to sublethal steam sterilization cycles at 120°C. The D-values were determined using the fraction-negative method. An increase in heat resistance (D-value) of 200%–400% was observed when the spore suspension was inoculated onto rubber stoppers. The D-values ranged from 4.90–6.96 minutes 120°C. No significant effect was seen when different preservatives were added to the stoppers nor when hot or cold rinse water temperatures were used after processing.