RAPID METHODS SUPPLEMENT


and/or false negative results, ease of use and validation. Sensitivity is one of the most critical factors to be considered in RMM investigation. The sensitivity is reflected by the minimum cell number of microorganisms that can be reliably detected. Due to the heterogeneity nature of microorganisms, the sensitivity of a RMM varies with different species of bacteria or even the physiological status of a single strain. The sensitivity of a reliable RMM should be scrutinised using a wide range of organisms with different cell sizes and/or different physiological status (healthy vs. stressed). Moreover, factory or facility isolates should be considered as these organisms may express phenotypic features peculiar to the microflora of potentially unique environments. The possibility of a false result is another important factor to consider. Occurrence of false positive or false negative results may take place due to technical limitations in a RMM. For example, in an adenosine triphosphate (ATP) bioluminescence based system, a false positive result could be attributed to a high ATP background level in a sample matrix, or even to static electricity generated in a dry environment (static charge can cause fluor molecules to become excited and yield UV-Visible light that is detected by the


photomultiplier tubes)14, while a false negative


result could be generated by a limited sample volume from a non-homogeneous cell suspension (typically mould which hyphae grow in bundles in a liquid medium), or insufficient ATP released from inadequate amount of cells below detection threshold. Autofluorescent particles could be falsely detected and counted along with bacterial cells by a fluorescence


the pharma ceutical microbiologist is the choice of precisely which technology to implement,


“The primary decision faced by


ensuring it fits the purpose of its desired or intended use”


detector. In a flow cytometry based RMM, a false positive result could be generated by cells that are dead but retain intact cell membrane and enzymatic activities. In a qPCR analysis, presence of extracellular nucleic acid fragments may lead to a false positive result. Contrarily, a false negative result could be generated by one or more of the following factors: the presence of sample residue affecting PCR reaction, insufficient DNA extraction, low quality of primers, and/or non-optimal conditions for the PCR reaction.


When determining the business benefit


from an RMM, the detailed evaluation should include capital and consumable cost, labour efficiency, time savings in generating results, authority acceptance, as well as supplier’s capability in technical support. The business benefit derived from a RMM is often considered the main motivation for application and implementation of the RMM. While RMMs tend to have higher operating costs than corresponding conventional methods, implementation of a RMM may result in substantial savings due to faster availability of data; realised in inventory reduction and labour efficiencies. An additional potential benefit for the patient may be achieved by releasing products (especially biologics) faster in turn extending shelf life by maintaining their expected potency and activity. It is imperative to carefully evaluate the benefits of a RMM through realistic and comprehensive calculations for return on investment4


. A supplier’s cooperation


and technical support is a key consideration for the successful implementation of RMM. To streamline the process of RMM


evaluation and selection, a decision matrix may be established based on the critical factors listed above. The decision matrix could be


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