What Auditors are Looking for in Food Microbiology Labs

by | Food | 2 comments

Publish Date: July 19, 2018

Audits are a fact of life for ISO 17025 food laboratories. Being prepared for an audit is important, but you may not know exactly what auditors are looking for when they review your microbial QC practices.

We’ve compiled a list of general requirements food laboratories must meet and QC best practices auditors want to see when they visit your facility. As your review our tips, keep in mind laboratories have different requirements based on the regulations they follow.


CRM = Certified Reference Material

RM = Reference Material

What requirements must food laboratories meet?

ISO 17025 specifies that “Reference materials shall, where possible, be traceable to SI units of measurement, or to Certified Reference Materials (section” Microbiologics Lab-Elite™ CRM (KWIK-STIK™ format) and Epower™ CRM are designed to help ISO 17025 laboratories meet the requirements of this standard.

Section 5.7.4 of ISO Guide 34 and 7.4.6 of ISO 17034:2016 states “The reference material producer shall ensure that the integrity of the individual reference material unit is maintained until the seal has been broken or up to the point when presented for analysis.” In the case of Microbiologics Epower CRM and Lab-Elite CRM products, the material is presented for analysis after the pellet is plated. Sub-cultured material from the CRM is no longer Certified Reference Material because the certified value and its uncertainty from the certificate are no longer applicable.

  • ISO 17025 laboratories need to use a new Lab-Elite CRM swab or Epower CRM pellet each time they are required to use CRM. Sub-cultures from the CRM cannot be considered CRM.
  • If the strain is frozen or sub-cultured, it is no longer CRM.

Growth promotion testing (GPT) must be performed per ISO 11133 and GMP. These chapters state “Test each batch of ready-prepared medium and each batch of medium prepared either from dehydrated medium or from the ingredients described.”

Many food microbiology laboratories consider a media “batch” to be any time a new lot number is used. This is an incorrect assumption. A media “batch” must be defined as:

  • Any new shipment of ready-prepared medium that is received in the facility, regardless of the lot number.
  • Any new batch of medium that is prepared from dehydrated culture medium, regardless of the lot number.

ISO 11133 (B.2) causes confusion by showing storage flowcharts for both reference strains (original strains from the culture collection) and reference stock (e.g., Microbiologics Lab-Elite and Epower CRM or KWIK-STIK RM) in Annex B. When using Microbiologics reference stock cultures, freezing is not required and in fact, is not recommended.

Why is this information important?

Media is purchased one of two ways:

1.  Purchased pre-made from the manufacturer. Manufacturers must prepare the agar under controlled conditions to avoid damaging the media. Storage and shipping conditions are vital to media quality through the expiry date. Factors to be considered vary between different types of media:

  • Temperature
  • Container (glass, plastic)
  • Humidity
  • Light

Shipping conditions can damage media quality. Regardless of the lot number, the shipment itself needs to be qualified for the media to be used for the intended test.

2.  Media prepared in-house. Raw materials (dehydrated media or the components) must be stored under appropriate and controlled conditions.

  • Raw materials must be used by the expiration date.
  • Dehydrated media must be prepared exactly in accordance with manufacturer’s instructions.
  • Sterilization of the media must be controlled and sterilized in accordance with the manufacturer’s instructions.

Key Takeaways

  • Laboratories following ISO 17025 and/or ISO 11133 must use a new CRM or RM each time they are required to use CRM or RM.
  • If a CRM strain is frozen or sub-cultured, it is no longer CRM.
  • Media QC is performed to ensure that each batch is performing within specification. Substandard media could lead to false negatives which could in turn lead to a recall. Media quality is one of the most essential functions of the laboratory. Make sure your laboratory is defining a “batch” of media correctly and spending the time to perform media QC properly.

Read Next: 5 Reasons to Avoid Maintaining Stock Cultures in Your Lab



Written by microbiologics

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  1. Wendy Jiménez

    Please, confirm if ready to use culture media that are tested by the manufacturer should also be tested after purchased and delivered to the laboratory?

    • Microbiologics

      Wendy – The decision on whether to test ‘ready to use’ culture media that has already been tested by the manufacturer must be determined by you and the specific regulations that you are following (or by the certifications and accreditations that your laboratory holds). For example, if you are following ISO 11133, then Growth Promotion Testing is required on any new shipment of ‘ready to use’ medium that is received into your facility (regardless of the lot number) and on any new batch of medium that you prepare from dehydrated culture medium (regardless of the lot number).


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