RNase III inSalmonellaEnteritidis enhances bacterial virulence by reducing host immune responses

Salmonellais an important foodborne pathogen which comprises strains that exhibit varied virulence phenotypes and the capability of causing invasive human infection. In this study, the gene expression profile of foodborne and clinicalSalmonellastrains that exhibit high- and low-level virulence was investigated, with results showing that the expression level of a number of genes, including therncgene which encodes the RNase III ribonuclease, were exceptionally high in the high virulence strains. Investigation of the role ofrncin mediating expression of virulence phenotypes inSalmonellashowed that the product of this gene could enhance expression of the superoxide dismutase SodA, which is an essential determinant of survival fitness ofSalmonellaunder the oxidative stress elicited by the host immunity. On the other hand, we also discovered that the double-stranded RNA (dsRNA) released fromSalmonellacould trigger immune response of the host, and that the high-level expression of therncgene enabledSalmonellato evade the host immunity by reducing the amount of dsRNA accumulated in the bacterial cell. These findings provide insightful understanding of the regulation ofSalmonellavirulence and facilitate development of novel antimicrobial treatments through suppression of virulence expression and survival fitness of this important pathogen.