Many times there is the desire to retest a sample when undesirable microorganisms are detected in a production lot. However, upon reanalysis, even when a larger sample size is used, the suspect organism cannot be detected in the retest analysis. One plausible reason can, of course, be lab error. However, many other reasons are equally plausible but require a better understanding of how microorganisms can enter into the production cycle. The following discussion includes concepts and examples based on years of experience at Deibel labs with product sampling and should aid you in understanding your retest results. Feel free to contact us for a further understanding of any of the following concepts.
Random and Non-Random Distribution of Microorganisms in a Production Lot
Example A. Microorganisms are distributed evenly throughout an entire lot of production, referred to as random or homogeneous distribution. In this case, microorganisms will likely be detected by random sampling of the production lot. This type of microbial distribution is not a factor of time since at any point in the sampling process there is an equal opportunity to detect the organism in question.
Example B. Microorganisms are not distributed evenly throughout an entire lot of production, referred to as non-random or heterogeneous distribution. In this case, microorganisms may not be detected by random sampling. This type of distribution is dependent on time since the microbial contamination is only represented at certain intervals in the production cycle without equal opportunity for detection.
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