With information about and control over the bioburden population and resistance, sterilization cycles requiring less time and temperature (relative to the overkill method) can be used successfully. The bioburden/biological indicator (BB/BI) method relies on the difference in resistance of the bioburden and BI (see Figure 2). The bioburden method requires detailed knowledge and control over the bioburden resistance and population. Sterilization processes are designed using one of three basic approaches (including the overkill method), each of which requires some degree of knowledge of the resistance and population of the bioindicator and bioburden (1). In the case of moist heat in which sterilization conditions are very well defined and understood, BIs are best used to establish that there is sufficient correlation between physically measured lethality, generally in the form of thermometric data, and biological lethality measured using calibrated BIs. Using these spores as indicator organisms creates a process challenge that is inherently worst-case. These BI organisms are stipulated to be spore populations that have much higher resistance to sterilization processes than the vegetative cells that predominate in the normal microflora found in pharmaceutical production environments. The microbial genera Geobacilli, Bacilli, and Clostridia, having substantial resistance to the sterilization process, are commonly chosen as BIs to provide an appropriate evaluation of the process. The difference in microbial resistance is critical to sterilization validation. The death curve for organisms exhibiting substantial resistance will have a shallow slope, and those with low resistance to the sterilization process will have a much steeper slope (see Figure 2). The slope of this line represents the resistance of the microorganism to the sterilization process. This phenomenon occurs with all microorganisms and is not restricted to any particular species. The death of microorganisms by any sterilization method has been shown to generally follow a straight line termed the "death curve" (see Figure 1). The difficulty lies in demonstrating the effectiveness of that process. While the probability may be reduced to a very low number, it can never be reduced to zero (2). Therefore, the number of microorganisms which survive a sterilization process can be expressed in terms of probability. In a sterilization process, the nature of microbiological death or reduction is described by an exponential function.
#OVERKILL DEFINITION FREE#
Sterilization as a process can be rather simply defined as:Ī validated process used to render a product free of viable organisms. This article reviews present sterilization practices and explores the difficulties inherent in this definition. This is not a lethality standard at all, however, because it inappropriately links the process lethality requirement to the characteristics of a specific biological indicator (BI).
What this definition suggests is that overkill requires a 12- D process, which equates to lethality sufficient to deliver a 12 × D 121 lethality level. Unfortunately, it cannot be demonstrated in a straightforward manner with presently available technology. This article focuses on steam sterilization, of which there is both a greater amount of published definitions and a more precise and generally accepted understanding of the underlying science.Ī contemporary definition of overkill moist-heat sterilization follows: "This is usually achieved by providing a minimum 12-log reduction of microorganisms having a D-value of at least one minute at 121 ☌" (1). Confusion associated with the overkill approach exists in all of the widely used sterilization technologies that is, moist heat, dry heat, gas, and radiation.
#OVERKILL DEFINITION HOW TO#
Although this is true, there is substantial confusion about how to use the overkill method and, in fact, regarding what actually constitutes an overkill process. It generally is considered to be the simplest and most straightforward method for the design and validation of moist-heat sterilization processes.
Overkill sterilization primarily is applied to the moist-heat processing of materials, supplies, and other heat-stable goods. The overkill method is perhaps the most common method used in the development and validation of sterilization processes.
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