Listeria monocytogenes in ready-to-eat (RTE) delicatessen foods: Prevalence, genomic characterization of isolates and growth potential

This study investigated Listeria monocytogenes prevalence and count in 132 ready-to-eat (RTE) delicatessen samples belonging to different categories (starters with/without mayonnaise pasta/rice-based courses, meat/ fish-based main courses) produced by an Italian industry. Whole Genome Sequencing characterized the iso-lates to map the pathogen circulation. Moreover, the growth potential of L. monocytogenes in the most contaminated product was investigated by a challenge test.L. monocytogenes was detected in 23 samples, giving an estimated prevalence of 17.4 %. Starters with mayonnaise showed a very high prevalence (56.7 %), showing the role of the sauce in the diffusion of the pathogen within the plant. A total of 49 isolates were obtained; they belonged to two different serogroups, IIb and IIa, and were related to two clonal complexes (CCs) and sequence types (STs) (CC288-ST330 and CC121-ST717), suggesting the possible persistence and circulation of the pathogen within the plant.The results of the challenge test showed a limited ability to grow in the selected product thanks to the presence of lactic microflora.