ISO 11133 and Media Preparators: How Do Food Microbiology Labs Handle the Concept of a Batch?

The recent release of products like the ReadyStream or instaBAG has brought back an existential question that’s crucial for all food microbiology laboratories: What is a batch?

This is a critical question, especially when it comes to ISO 11133, which (to put it simply) requires microbiologists to test the performance of each batch of culture media.

Those performance tests (fertility tests) require time and resources, so for the lab workload, it is always better to reduce their frequency.

Given the complexity of this issue, we turned to accredited laboratories that use media preparators to find out how they “manage” this standard.

Here’s what they had to say:

Accredited labs, Media Preparators and ISO 11133

We interviewed three accredited laboratories that produce large volumes of culture media (mainly enrichment broths like EPT) using culture media preparators.

How do they handle the concept of a batch and ISO 11133?

The concept of a batch varies slightly among them. However, a media preparator cycle is not considered a batch.

In other words, they do not perform performance tests for every media preparator cycle.

“We had hoped the labs could explain publicly how they justify their definition of a batch… But the topic is so ‘touchy’ that none of them wished to do so (which we completely understand!).”

That said, they were incredibly transparent with us (and we’re very grateful for that), so we’ll try to provide some insights and food for thought.

What does ISO 11133 says about the concept of batch?

Tous les laboratoires de microbiologie alimentaire peuvent suivre la norme ISO 11133, mais elle n’est obligatoire que pour les laboratoires accrédités COFRAC.

Voici ce qui est écrit dans le guide du COFRAC, le LAB GTA 59 : 

“3.1.2 Batch of culture medium

A unit of homogeneous medium that meets traceability requirements, corresponding to a defined quantity of bulk products, semi-finished or finished products, of uniform type and quality, produced during a specific period and identified under the same batch number.“

As with any standard, there can be different interpretations.

Let’s now look at how the labs we questioned justify the fact that one media preparator cycle is not equal to one batch!

How to justify that a media preparator cycle is not equivalent to a batch

For these laboratories, the justification lies in a comprehensive risk analysis that encompasses:

• the dehydrated powder
• the water quality
• the media preparator cycle parameters
• the technician qualifications
• the internal controls.

A batch is therefore defined as a combination of elements that must be controlled to ensure homogeneous production.

1 – Dehydrated Media

The laboratories interviewed each have a different strategy, but in all cases, a batch does not correspond to a batch of dehydrated powder.

For some, performance tests are carried out with every new container of dehydrated powder, while for others, they are conducted every three months, regardless of whether the container is finished or not.

2 – Water Quality

The key question to ask is: what impact can water have on the quality of my culture media?

Without being exhaustive, here are a few points to consider:

• Presence of residual chemical molecules that could inhibit microorganism growth.
  For example: testing for pesticides.
  
• Significant contamination that might not be eliminated during the sterilization cycle.
  For example: testing for bacterial load.

For each of these issues, it is essential to implement controls at a defined frequency to demonstrate proper management.

3 – Media Preparator Cycle Parameters

This is perhaps the easiest information to obtain. It simply requires verifying that the cycle parameters, such as time and temperature, have been properly followed.

Most media preparators are designed to provide this level of traceability. However, this depends on ensuring that the sensors are correctly calibrated… but that’s another issue entirely!

4 – Technician Qualification

Producing culture media involves several steps, some of which are more critical than others. These steps are performed by technicians who must be properly trained for the task.

Here are some non-exhaustive examples of critical points: 

• Weighing the powder (this can be documented and traced with a balance ticket).
  
• Filling the tank with water (this can be critical if the water volume is not respected and no traceability exists).
  
• Cleaning the tank between productions (to prevent chemical or microbiological contamination).

Some steps can be traced automatically by machines (e.g., a weighing ticket from the balance), while others cannot (relying on human traceability).

This is why proper training and qualification of technicians are crucial.

Internal Controls

All the labs we interviewed perform a blank test for every media preparator cycle, i.e., a negative control. This involves taking a sample of the culture media, incubating it, and ensuring it shows no contamination.

When it comes to internal positive controls, strategies vary. Some labs conduct them frequently, others less so, and some not at all.

Regular positive controls, using strains of interest at very low concentrations, allow for verification of the media’s performance and its ability to support microbial growth under specific conditions.

Conclusion

In conclusion, the question of defining a batch in food microbiology remains complex and subject to various interpretations. Accredited laboratories using media preparators adopt different approaches to address this concept.

Some consider each media preparator cycle as a distinct batch, while others assess the overall control of the production process to define a batch.

Factors such as cycle parameters, water quality, staff qualifications, and internal controls play a critical role in this justification. Each lab tailors its method based on its specific risk management strategy.

There is no single answer, and ISO 11133 must be approached with a critical and contextual perspective to ensure the quality of culture media in food microbiology.

Share your interpretation of ISO 11133 in the comments below!