Pharmaceutical Regulatory Affairs: Open Access

Current Mistaken Interpretation of Microbiological Data on Gas Plasma Sterilization

Abstract

Hideharu Shintani

Even when using vegetative cells, a tailing phenomenon can be observed in survivor curves in engineering researcher’s papers on gas plasma sterilization. This indicates that even disinfection was not even achieved. By definition, sterilization is a process that kills all types of microorganisms including bacterial spores and vegetative cells. In contrast, disinfection kills only vegetative cells and does not kill bacterial spores. Tailing of a survivor curve is often caused by clumping of the biological indicator (BI), and engineering researchers who make their own BI without critical knowledge, appropriate techniques and confidential know-how to avoid such clumping frequently publish nonlinear survivor curves. Preparation of a monolayer of BI is quite a difficult task even for BI manufacturers and it requires proprietary information. Therefore, engineering researchers should purchase commercially available BI. Among the BIs on the market, I recommend purchasing BI from Merck Co., as clumping was found to be minimal based on results of scanning electron microscopy (SEM) observation. When such a tailing phenomenon is observed, a SAL of 10^-6 cannot be attained, and therefore no D value (decimal reduction value) can be determined and the exposure time for a 9 or 12 log reduction remains undefined. The D value must be determined from the straight line of a 9 log or 12 log reduction survivor curve, and there can only be one D value per microorganism; there is never more than one D value per one microorganism. The BI is defined as the most tolerant microorganism (typically bacterial spores) to the sterilization procedure being used, so if the BI is killed, then other contaminants (microorganisms) can be speculated to also be killed. Therefore, the use of a BI is essential in sterilization validation studies and routine control. Strategies to avoid clumping, tailing phenomena and to attain a SAL of 10^-6 will be considered in this article.