Environmentally regulated genes of Streptococcus suis: identification by the use of iron-restricted conditions in vitro and by experimental infectionof piglets

The identification of environmentally regulated genes of Streptococcus suis by the use of iron-restricted conditions in vitro and by experimental infe ction of piglets is described. Eighteen unique iron-restriction-induced (ir i) genes and 22 unique in-vivo-selected (ivs) genes of Strap. suis were fou nd. None of the ivs genes was exclusively expressed in vivo. Four iri genes were identical to four clones selected in piglets. Two ivs genes were simi lar to genes for putative virulence factors. One of these ivs genes was ide ntical to the epf gene of virulent Strep. suis serotype 2 strains and the o ther showed homology to a gene encoding a fibronectin-binding protein of St reptococcus gordonii. Two additional ivs genes showed homology to environme ntally regulated genes previously identified by using an in vivo expression technology (IVET) selection system in other bacterial species. One of thes e showed similarity to the agrA gene of Staphylococcus aureus, a key locus involved in the regulation of numerous virulence proteins. The promoter sel ection system described in this paper has been successfully used for the id entification of many environmentally regulated genes potentially involved i n the pathogenesis of Strap. suis infections in piglets.