Salmonella Serotyping Free of Charge

Salmonella isolates from the food production chain are a valuable source of information to the Food Standards Agency.  The Agency strongly encourages plants to send any Salmonella isolated when testing against the microbiological criteria to one of the serotyping reference laboratories listed so that the strain and type of Salmonella can be determined.  Detailed instructions for using the free serotyping service can be found here.  A summary flowchart that describes the process is shown below:

Figure 1: A summary flowchart that demonstrates how the free Salmonella serotyping service operates.

It is important to stress that:

Sending an isolate for typing is not an obligation and it will not trigger any sort of enforcement from the FSA, Defra, or your OV.

Most of the time, apart from letting you know the results of the typing of your strains, there would be no contact with plants.  The only contact that may be undertaken (and this would be in a very few cases, if at all) would be investigatory (i.e. nothing at all to do with enforcement) in nature if, for example, a very rare and or previously unseen type was isolated.  By providing isolates for testing you will however be assisting in the provision of information that will be made available for risk assessments on the appropriateness of Salmonella test criteria for raw meat and you may also find the results useful for investigating the source of the contamination.

During the development of the criteria it was apparent that there was a lack of typing information on Salmonella isolates from the food production chain in comparison with the amount of information available on isolates from humans.

This process will not cost your plant or your testing lab any money because the FSA will pay all of the costs associated with these additional tests -including a small payment to the isolating laboratory to cover their administrative costs.  Instructions for your laboratory that explain how to have an isolate serotyped are available here. 

Plant operators will be able to see the results of the additional serotyping tests by logging into the meat test results database.  It is hoped that eventually a picture can be built up of commonly-isolated Salmonella from meats and that the primary sources of these isolates can be identified.   An assessment of how dangerous the Salmonella isolates are will also be made available to plant operators through the meat database.

The majority of Salmonella isolated from livestock are not human pathogens.   There is no legal obligation for plants to send their isolates for serotyping, but those that do so will be contributing to an "appropriateness of testing" review in 2009 which may remove the testing requirement (but there is no guarantee that will happen!).

Serotyping of meat is performed according to a slightly modified method to that originally developed by Kauffman and White ⁽¹⁾.

The process involves using antibodies (and sometimes bacterial viruses called phages) which selectively recognise specific structures on the outside of the Salmonella cells.  These external structures are called antigens and there are three main types used for Kauffman and White method of Salmonella typing.  The main antigens are the O-types, the H-types and the Vi-types.  Not all Salmonella have all three of these types of antigen.  The combination of O-type, H-type and Vi-type antigens recognised by the antibodies and phages allows the serotype to be identified. 

For example, a Salmonella that is commonly isolated from foods is called Salmonella enterica.  Within Salmonella enterica there are a large number of serotypes.  Some of these are given in the table below

Table 1:  Commonly-encountered Salmonella enterica serotypes

In time, it is hoped that plant-derived data can, along with other Salmonella isolations be used to generate graphical figures such as the one below.  Such graphical representations allow "hotspots" of Salmonella to be identified and also allow "tracking" of the movements of specific Salmonella serotypes over time. 

Figure 2:  (A FICTITIOUS EXAMPLE).  A graphical representation of Salmonella enterica serotype Dublin isolated from Southern Scotland in 2005

In the long term such information may be used to help develop intervention strategies which will help further reduce foodborne illness caused by Salmonella in the UK.  A postcode of the farm that livestock were farmed on, and the plant where the Salmonella were isolated is required for construction of such graphical representations.  This is the only reason the Agency requests the farm or plant postcode is supplied for each isolate that is serotyped.

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References

1. Popoff, Y. Antigenic formulas of the Salmonella serovars, 8th revision. Paris: WHO Collaborating Centre for Reference and Research on Salmonella, Institut Pasteur; 2001.