Growth of Listeria Monocytogenes in ready to eat salads at different storage temperatures and valuation of virulence genes expression

BACKGROUND: Vegetables are major components of a healthy and balanced diet. However, 25% of foodborne diseases are linked to the consumption of vegetables. STUDY DESIGN: The aim of this work was to assess the microbiological risks associated with consumption of ready to eat salads (RTE). METHODS: Microbiological challenge tests were carried out for the evaluation of the L. monocytogenes growth potential in RTE salads stored at different temperatures. RESULTS: The results indicate that L.monocytogenes was able to grow (δ ≥ 0.5) in all storage conditions considered at the end of shelf life. In order to evaluate the virulence role of L. monocytogenes, the temperature-dependent transcription of major virulence genes was also investigated by RT-PCR. CONCLUSIONS: The microbiological challenge test allowed us to confirm, as also demonstrated by other authors, that RTE salads are able to support the growth of L. monocytogenes strains (d δ≥ 0.5) stored under different temperatures.