A simple model host for identifying Gram-positive virulence factors

We demonstrate the use of the nematode Caenorhabditis elegans as a facile a nd inexpensive model host for several Gram-positive human bacterial pathoge ns. Enterococcus faecalis, Streptococcus pneumoniae, and Staphylococcus aur eus, but not Bacillus subtilis, Enterococcus faecium, or Streptococcus pyog enes, kill adult C elegans. Focusing our studies on the enterococcal specie s, we found that both E. faecalis and E. faecium kill C elegans eggs and ha tchlings, although only E. faecalis kills the adults. In the case of adults , a low inoculum of E, faecalis grows to a high titer in the C elegans inte stine, resulting in a persistent infection that cannot be eradicated by pro longed feeding on E. faecium. Interestingly, a high titer of E. faecium als o accumulates in the nematode gut, but does not affect the longevity of the worms. Two E. faecalis virulence-related factors that play an important ro le in mammalian models of infection, tsr, a putative quorum-sensing system, and cytolysin, are also important for nematode killing. We exploit the app arent parallels between Gram-positive infection in simple and more complex organisms by using the nematode to identify an E. faecalis virulence factor , ScrB, which is relevant to mammalian pathogenesis.