The Effect of Carrier Material on the Measured Resistance of Spores - Pharmaceutical Technology

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The Effect of Carrier Material on the Measured Resistance of Spores
A biological indicator (BI) measures the effectiveness of the sterilization process to which it is subjected. Factors such as the test organism, the packaging, the culture material, and the test system all influence a BI's resistance. Carrier material is an often-overlooked factor that also influences BI resistance. The authors examine various solid and liquid carriers, describe their properties, and investigate how they influence BI resistance.

Pharmaceutical Technology

Table III: Summary of D-value study results on biological indicators using liquid pharmaceutical products and water for injection (WFI) as the spore carrier.
Commercially available BIs designed to monitor sterilization processes should be correlated to the spore-resistance characteristics of the products that they monitor. This correlation will ensure the most appropriate challenge to the sterilization process. Ideally, the spore carrier of the BI should be composed of materials similar to those processed in the sterilizer. If this situation is not feasible, D-value studies can be performed on component materials in the load to determine the substrate effect of the load. Once the substrate effect is known, an appropriate BI can be selected and correlated to the process.

Kurt McCauley is the research and development laboratory manager and John R. Gillis, PhD,* is the president and CEO of SGM Biotech, 10 Evergreen Dr., Suite E, Bozeman, MT 59715, tel. 406.585.9535, fax 406.585.9219,

*To whom all correspondence should be addressed.

Keywords: biological indicator, carrier material, resistance, spore suspension


1. American National Standards Institute, ANSI/AAMI/ISO 14161: Sterilization of Health Care Products—Biological Indicators—Guidance for the Selection, Use, and Interpretation of Results (ANSI, Washington, DC, 2000).

2. V. Sigwarth and A. Stark, "Effect of Carrier Materials on the Resistance of Spores of Bacillus stearothermophilus to Gaseous Hydrogen Peroxide," PDA J. Pharm. Sci. Technol. 57 (1), 3–11 (2003).

3. H. Shintani and J.E. Akers, "On the Cause of Performance Variation of Biological Indicator Used for Sterility Assurance," PDA J. Pharm. Sci. Technol. 54 (4), 332–341 (2000).

4. J.A. Terezina, T. Pinto, and I. Mario, "Ethylene Oxide Sterilization: III—Influence of Carrier Nature in a Biological Monitor Performance," PDA J. Pharm. Sci. Technol. 48 (3), 155–158 (1994).

5. I.J. Pflug, Microbiology and Engineering of Sterilization Processes (Environmental Sterilization Laboratory, Minneapolis, MN, 11th ed., 2003).

6. G.A. Mosley and C.W. Houghtling, "Interpreting and Understanding Microbial Data in Validation of Ethylene Oxide Sterilization Processes," Biomed. Instrum. Technol. 39 (6), 466–482 (2005).

7. S. Hury et al., "A Parametric Study of the Destruction Efficiency of Bacillus Spores in Low Pressure Oxygen-Based Plasmas," Lett. Appl. Microbiol. 26, 417–421 (1998).


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