RNase III in Salmonella Enteritidis enhances bacterial virulence by reducing host immune responses

Salmonella is 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 clinical Salmonella strains that exhibit high- and low-level virulence was investigated, with results showing that the expression level of a number of genes, including the rnc gene which encodes the RNase III ribonuclease, were exceptionally high in the high virulence strains. Investigation of the role of rnc in mediating expression of virulence phenotypes in Salmonella showed that the product of this gene could enhance expression of the superoxide dismutase SodA, which is an essential determinant of survival fitness of Salmonella under the oxidative stress elicited by the host immunity. On the other hand, we also discovered that the double-stranded RNA (dsRNA) released from Salmonella could trigger immune response of the host, and that the high-level expression of the rnc gene enabled Salmonella to evade the host immunity by reducing the amount of dsRNA accumulated in the bacterial cell. These findings provide insightful understanding of the regulation of Salmonella virulence and facilitate development of novel antimicrobial treatments through suppression of virulence expression and survival fitness of this important pathogen.