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Appendix

Published online by Cambridge University Press:  21 June 2016

Extract

The performance of a biological indicator (BI) over a range of sterilization temperatures is known as a z value and, as defined by Roberts, is “the number of degrees change in temperature to achieve a tenfold change in the D value.” A plot of the D values versus exposure temperatures will reveal the z value as the negative reciprocal of the slope of the resulting thermal resistance curve. Historically, paper strip carriers of Bacillus stearothermophilus spores have been found to possess a z value in the range of l7°-2O°F, whereas self-contained BIs tested in our laboratories have exhibited z values as high as 64°F (Figure I), which reflects their excessively high resistance at flash sterilization temperatures. In general, such matters are not of concern to the end user until such time as false positives are encountered during flash sterilization.

Type
Original Articles
Copyright
Copyright © The Society for Healthcare Epidemiology of America 1988

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References

1. Roberts, TA, Hutchins, AD: Resistance of spores, in Gould, GW, Hurst, A (eds): The Bacterial Spore. New York, Academic Press, 1969, pp 611670.Google Scholar
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3. American National Standard. Biological Indicators for Saturated Steam Sterilization Processes in Health Care Facilities. 1985. Association lot the Advancement of Medical Instrumentation.Google Scholar
4. Pharmacopeial Forum. In-Process Revision. Sept-Oct. 1985. The United States Pharmacopeial Convention, Inc. pp 64806485.Google Scholar
5. Pflug, IJ: Heat sterilization, in Phillips, GB, Miller, S (eds): Industrial Sterilization. Durham, NC. Duke University Press. 1972. pp 239282.Google Scholar