Development and validation of stable reference materials for food microbiology using Bacillus cereus and Clostridium perfringens spores

To develop a new type of microbiological Reference Materials (RMs),
displaying long-term stability at room temperature. The purpose was to produce
and validate two batches of RMs for the enumeration of Bacillus cereus and
Clostridium perfringens.
Methods and Results: The RMs were based on spores of B. cereus and
Cl. perfringens, adsorbed on calcium carbonate pellets. Two batches of 1000 units
were manufactured and validated in compliance with ISO guide 35. After
verification of their homogeneity, the stability of the ‘RM-B. cereus’ and ‘RMCl.
perfringens’ batches was proven during at least 36 and 9 months, respectively,
at room temperature. The validation study was completed by international
collaborative trial involving 12 laboratories, allowing the validation of the
assigned values.
Conclusions: The methodology developed in this work enabled to produce
easy-to-handle and cost-effective RMs, displaying an unprecedented stability at
room temperature, a good homogeneity and a precise and validated assigned
value.
Significance and Impact of the Study: This study revealed new paths for the
development of stable microbiological RMs. Overcoming the intrinsic instability
of the living cells makes it possible to produce valuable tools for the quality
assurance of microbiology laboratories.
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