CRM with UV tag

Biosisto has frequently asked whether we can supply CRM with a UV tag in the past year. Biosisto does not have these products because working with GMMO (Genetically Modified Organisms and Micro-organisms) is linked to European regulations, and we currently do not comply with this. The laboratories that use CRM + UV tags must also comply with these regulations. From inquiry, we know that most of our customers do not have this permit.

Why use CRM with a UV tag?

All alarm bells often go off immediately when a pathogen is found in an investigated product. The laboratory wants to be able to say quickly and with certainty that the pathogen is actually in the product and that it was NOT accidental cross-contamination of the CRM. A CRM + UV tag growing on an agar plate can easily be distinguished from a pathogen in a product by placing the plate under a UV lamp. The CRM + UV tag colonies will light up while the pathogen isolated from a product should not. CRM + UV tags are already available outside Europe. The regulations outside Europe are more flexible.

More information about the assessment of genetically modified microorganisms can be found on www.rivm.nl.
More information about a GMO Permit can be found on GGO-vergunningenverlening.nl.

Biosisto understands the need for laboratories to quickly clarify the origin of the pathogen found. Biosisto would like to think along and find a solution to support and help its customers in this.

Alternatively, for the Internal Quality Control of the Salmonella analysis, a non-food-related strain can be used for the Salmonella analysis, such as CRM-STRAN and CRM-SABEA.

If you do not find black colonies, or fewer colonies, on the agar plate by the analyses of Clostridium perfringens or Sulfite-reducing bacteria, it can have several causes.
Checking the below items in your laboratory to solve the issue.

1. Media and filter (for water analysis) must be fit for purpose

For food analyses, these performances and criteria are:
ISO 7937 Media performance test TSC (SC)
ISO 15213-1 Media performance test ISA (IS or ‘TS’)

For water analyses, these performances and criteria are:
ISO 14189 Media performance test TSC
ISO 6461-2 Media performance test Sulfite Iron – Tryptose Sulfite (TS)

Did you perform a membrane filter validation according to ISO 7704?
The combination of media with filter must give a good performance.

If the media and or membrane filters are not fit for purpose, try to use a different batch of media or filter. Or try another media of membrane filter supplier.
Media from supplier to supplier can give different results in appearance and productivity.

For example:
CRM-CP was analyzed simultaneously on TSC (SC) media of 3 different suppliers according to ISO 7937.
The appearance of the TSC (SC) agar was different. One media, the Clostridium perfringens, is more enthusiastic with the black coloring than the other.
See the examples below of 3 different media suppliers.

Colorless colonies on ISA – a practical example
The reference material CRM-CP on ISA medium incubated for 24h at 37°C anaerobic gave no black colonies by a specific media lotnumber. However, not all the bottles of ISA give colorless colonies.
Some bottles are given black, and others of the same lotnumber of ISA give colorless colonies.
Another laboratory also found this phenomenon using the same ISA with the same lot number.
Inquiries with the supplier about the cause of this phenomenon could not find an explanation.

2. Media overlay for better black coloring

Cultures not overlaid with agar will have no or poor black colonies despite incubation under anaerobic conditions.
Some examples you will find below.

TSC (SC) with and without an overlay                            

TSC with and without an overlay

Sulfite Iron-Trypose Sulfite (TS) with and without an overlay

3. Incubation must be under anaerobic conditions

The incubation must be performed under anaerobic conditions. Ensure incubation conditions are correct.
You can check the anaerobic jar with an anaerobic indicator strip.

4. Heat treatment for the anaerobic spore in food analyzes

CRM-CPE.00007MH contains viable spores that survive a heat treatment of the first 1:10 dilution.
It turns out that when a higher dilution is pasteurized, the spores have a lower yield.
Therefore, it is recommended to carry out the heat treatment with a dilution not higher than 10x.

5. Diluent used in the heat treatment is crucial for a good yield by spore in water analyzes

Dilutions of CRM-CPE.0007BL is often made in water. Research has shown that different types of water can give different yields.
By Biosisto, softened water gave a significantly lower yield of spores. It is recommended to check with your laboratory whether this is the case. 

Biosisto strongly advises storing the CRM at a temperature of -80˚C. Only when using this storage temperature, the concentration on the Certificate is valid and the CRM is guaranteed stability.

You can download the Certificate of Analysis:

At https://www.biosistochart.com/login

If you are logged in, you can find the Certificate under the menu ‘Chart Setup’

1. Choose ‘Batch certificates’
2. Search for product and batch

If you do not (yet) have an account, the Certificate can be found under the button ‘View Batch Certificates’ or the button ‘Certificates’ on the start page.

1. Go to the product and type and search the batch number or product name
2. Search for product and batch

At www.biosisto.com

1. Go to Certificates
2. Search for product and batch

All certificates are always available electronically.

When the method is precisely the same as described on the Certificate, you can compare the results with the property value on the Certificate of Analysis. Another technique, media, or incubation temperature, can give other effects and can provide another result.

Checklist for root cause analyses:

1. Media – the most common cause of differences

Check if the used media and possibly used filters fit your purpose. Therefore, performance testing of culture media according to ISO 11133 and performance testing of membrane filters according to ISO 7704 can be performed.

Search on the BiosistoStandard, which controls must be used as a minimum.

2. Incubation

Check the incubation temperature and time to see if they are correct.
Some microorganisms are sensitive to temperature. If the temperature of an incubator is set just a little too high, this can result in no growth

3. Used equipment

Check if the used equipment is fit for the purpose. For example, is the pipette calibrated?

4. frequency

How often does this problem occur? Is this structural, or is it an incident issue?

5. Comparison with other labs

How do your results compare with other laboratories? An easy way to compare your results with other laboratories is to use the BiosistoChart. Ask for a free account

If you cannot find a cause for the deviating CRM value as a result of the above questions, please do not hesitate to contact Biosisto.

Biosisto has five different types of CRM Salmonellae in stock. The choice depends on the laboratory’s requirements and what the laboratory prefers.

In the table below, you will find the differences per Salmonella.

* MLVA Multiple Locus Variable-number Tandem Repeat Analysis

Find more information in the related articles below.