SmcL, a novel membrane-damaging virulence factor in Listeria

We describe here the fourth listerial membrane-damaging virulence factor, a sphingomyelinase C (SMase) that is produced specifically by the ruminant p athogen Listeria ivanovii. Its coding gene, smcL, is a monocistron expresse d independently of PrfA. The smcL product, SmcL, is highly similar to the s taphylococcal B-toxin and is responsible for the differential hemolytic pro perties of L. ivanovii (bizonal hemolysis and CAMP-like reaction with R. eq ui). The role of SmcL in virulence was assessed by gene disruption and comp lementation. Our data show that SmcL mediates disruption of the membrane of primary phagosomes, thereby promoting bacterial intracellular proliferatio n. They also suggest that SmcL may play a role in host tropism. smcL is loc ated in LIPI-2, a novel 18-kb pathogenicity island which also contains a cl uster of internalin genes. LIPI-2 is unstable, L. ivanovii-specific and req uired for full virulence in mice and lambs.