Enhancement of the pathogenicity of Staphylococcus aureus strain Newman by a small noncoding RNA SprX1

The pathogenesis of Staphylococcus aureus from local infection to systemic dissemination involves a range of virulence factors including structural and secreted products. Among various control mechanisms, small noncoding RNAs are involved in the regulation of multiple pathogenicity factors in S. aureus. The sRNA SprX which is encoded in the pathogenicity island of methicillin-susceptible S. aureus strain Newman and was shown to influence antibiotic resistance previously, upregulated the expression of virulence genes, especially the cell wall-associated clumping factor B (ClfB) and delta hemolysin (Hld). Bioinformatic analysis revealed several multiple mRNAs associated with pathogenicity as targets for SprX1, one of the three copies of sprX. Both overexpression and chromosomal disruption of sprX1 supported the scheme of upregulation of clfB and hld expression. Altered expression of SprX1 altered the levels of Hld and ClfB mRNAs, hemolysis, clumping of cells, biofilm formation by plate adhesion studies and confocal microscopic analysis as well as infection pathology of modified strains in mice models. ClfB and Hld mRNAs interacted directly with SprX1 in in vitro assays. Increased level of the regulatory RNA, namely RNAIII, that comprises Hld mRNA and also regulates the biofilm formation, indicates that SprX1 may also function through RNAIII for regulating virulence factors. An immunodominant protein, antigen A, was downregulated by SprX1 in two-dimensional electrophoresis. Taken together, these results signify the role of sRNA SprX in the pathogenicity of S. aureus Newman.