PLASMID-MEDIATED VIRULENCE GENES IN NONTYPHOID SALMONELLA SEROVARS

Specific non-typhoid Salmonella serovars carry large virulence plasmid s that promote sustained extra-intestinal infections. These plasmids a ll share a highly conserved 8-kb region containing the spv operon, con sisting of the regulatory spvR locus and the four structural spvABCD g enes. The SpvR protein belongs to the LysR/MetR family of transcriptio nal activators, and induces spvABCD expression in the stationary phase in response to nutrient limitation. spv expression also depends on th e chromosomal stationary phase sigma factor RpoS (KatF), and is marked ly induced when salmonellae enter eukaryotic cells. Additional plasmid genes encode complement resistance including the rck locus which is h omologous to ail from Yersinia. Rck blocks formation of the complement membrane attack complex on the bacterial surface. Several loci involv ed in plasmid replication and stable maintenance have also been identi fied.