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Reference materials

Definitions of reference materials (RM) and certified reference materials (CRM) according to ISO Guide 30

Reference material (RM)

A material or substance of wich one or more properties is/are sufficiently well established to be used for the calibration of apparatus, the assessment of a measurement method or to assignment of values to materials.

Certified reference material (CRM)

A reference material, one or more of wich the property values are certified by a technically valid procedure and accompanied by, or traceable to, a certificate or other documentation issued by a certifying body.

From 1986 up to 1995, the Microbiological Laboratory for Health Protection (MGB) of the Dutch National Institute for Public Health and the Environment (RIVM) led EU funded projects on the development and certification of microbiological reference materials. The experience and the knowledge obtained from these projects have been applied in preparing reference materials for use as standard samples in the interlaboratory comparison studies of the EURL-Salmonella.
The reference materials are prepared as follows:

  • A selected strain is cultured and mixed with milk
  • This milk suspension is spray-dried, resulting in a highly contaminated milk powder (hcmp). Which is then stored at -20 ºC
  • A small portion of the hcmp is mixed with sterile milk powder until the desired contamination level
  • The mixed powder is put into gelatin capsules, resulting in the final reference materials (to be stored at -20 ºC)

The first certification studies on microbiological reference materials were organised in 1992, resulting in the successful certification of 6 batches of reference materials:

  • CRM506 Enterococcus faecium
  • CRM507 Salmonella Typhiumurium
  • CRM527 Enterobacter cloacae
  • CRM528 Bacillus cereus
  • CRM594 Escherichia coli
  • CRM595 Listeria monocytogenes

These CRMs are available at the Institute for Reference Materials and Methods (IRMM) of the Joint Research Centre (JRC) in Geel, Belgium.

After their development, the non-certified reference materials were produced for some years by the Foundation affiliated to the RIVM. This production stopped in 2003. Today several other institutes or (commercial) manufacturers also produce and sell microbiological reference materials, e.g. Institute Pasteur in France and Health Protection Agency in the UK.