Manuscript Highlights  Listeria monocytogenes is a foodborne opportunistic bacterial pathogen  Classical genetic approaches in reference strains allowed identification of core virulence genes  Investigation of the species diversity of L. monocytogenes allowed uncovering hypoand hypervirulent strains and new virulence genes  Hypervirulent strains are host-associated, whereas hypovirulent strains are associated with food-processing environments  Accumulation of loss-of-function mutations in virulence pathways leads to niche restriction and obligate saprophytism