FLUORESCENCE-BASED ISOLATION OF BACTERIAL GENES EXPRESSED WITHIN HOST-CELLS

A selection strategy was devised to identify bacterial genes preferent ially expressed when a bacterium associates with its host cell. Fourte en Salmonella typhimurium genes, which were under the control of at le ast four independent regulatory circuits, were identified to be select ively induced in host macrophages. Four genes encode virulence factors , including a component of a type III secretory apparatus. This select ion methodology should be generally applicable to the identification o f genes from pathogenic organisms that are induced upon association wi th host cells or tissues.