[Foodborne Listeria monocytogenes: are all the isolates equally virulent?]

Listeria monocytogenes is a foodborne human pathogen responsible for invasive infections presenting overall a high mortality. Despite the ubiquity of the microorganism, the actual disease rate is quite low and the disease is most often associated with an underlying predisposition. Foodborne and environmental isolates were traditionally considered of similar pathogenicity compared to clinical isolates. But the analysis of mutations in the genes encoding specific virulence factors (internalin, hemolysin, phospholipases, surface protein ActA and regulator protein PrfA), quantitative studies with cell cultures and population genetics have raised considerable concerns about virulence differences among L. monocytogenes strains. Despite this great step forward, there is not a single marker available to test the virulence of field isolates of this species. In the future, the combination of different molecular markers will probably allow the screening of food contamination by only the virulent clones of L. monocytogenes, thus improving the prevention of foodborne human listeriosis.