Selection of Bacterial Virulence Genes That Are Specifically Induced in Host Tissues

A genetic system was devised that positively selects for bacterial genes that are specifically induced when bacteria infect their host. With the pathogen Salmonella typhimurium, the genes identified by this selection show a marked induction in bacteria recovered from mouse spleen. Mutations in all ivi (in vivo-induced) genes that were tested conferred a defect in virulence. This genetic system was designed to be of general use in a wide variety of bacterial-host systems and has several applications in both vaccine and antimicrobial drug development.