The EURL for Listeria monocytogenes  (Lm) together with the Italian, the Hungarian NRLs and the Dutch associated NRL have developed a PCR test for the rapid and inexpensive (10€ reagent cost) identification of 30 Lm strains Multi locus sequence typing clonal complexes (CC). It has already been used in Greece, Italy, the Netherlands and Hungary to investigate the origin of human cases of listeriosis. 

The project was conducted by a working group of 11 NRLs (BE, CH, CY, DE, IT, NL (RIVM and WFSR), PT, SK, SE, SI) that shaped the method to fit with their needs. 

This is a significant step forward compared with the method normally used, multilocus sequencing typing (MLST), which requires three to five days of analysis and costs €150 per strain tested. 

Already four training sessions were organised on the method for the NRLs CY, GR, HU, MK, PT, XK. The EURL Lm re-conducts every year the budget to finance their organisation. 

Identify the 30 most common strain groups

"The test we have developed can identify the 30 Listeria monocytogenes CC, known as clonal complexes, most commonly found in food in Europe" explains Benjamin Félix, project leader of the EURL for Lm. "Our method is very useful for countries that don't have the financial resources to carry out routine sequencing of whole genomes, or when a large number of samples need to be analysed, as it can be used to quickly make an initial selection." 
This new method was published in the journal Microbiology Spectrum in May - link.

An example of its use: fish-based products responsible for listeriosis in the Netherlands
Reference laboratories in several European countries have already been trained in this new method, showing its value in real-life situations. For example, the Dutch food safety authority used the test to determine the source of listeriosis cases that have been reported in the last few years. Two manufacturers of fish-based products were suspected of being behind the contamination. Samples were taken from areas of the plants most at risk of contamination, such as cutting machines, trays and conveyor belts. Thanks to the speed and low cost of the PCR test, it was possible to run 200 analyses in order to select six strains for priority sequencing. This then identified the plant responsible for the contamination.