Staphylococcus aureus Extracellular Vesicles Enhance PslE-Mediated Pathogenesis in Pseudomonas aeruginosa

Coinfection of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) is frequently observed. Our previous study demonstrated that S. aureus-derived extracellular vesicles (SaEVs) promote P. aeruginosa pathogenicity by increasing lipopolysaccharide (LPS) production, promoting biofilm formation and decreasing the uptake of P. aeruginosa by macrophages. Proteomic analysis revealed that SaEVs enhance the production of PslE, an exopolysaccharide biosynthetic protein in P. aeruginosa, but the role of Psl exopolysaccharide polymerization on SaEV-mediated P. aeruginosa pathogenicity is unclear. In this study, a pslE-deletion mutant of P. aeruginosa (PaΔpslE) was constructed, and the effect of SaEVs on the pathogenicity of this mutant was evaluated. Our results showed that SaEVs significantly increased the expression of pslA, E, J, K, and L genes in the psl cluster of P. aeruginosa wildtype (PaWT), and this effect was abolished in PaΔpslE. In addition, LPS production and biofilm formation were reduced in PaΔpslE compared to PaWT. SaEVs significantly enhanced LPS production and biofilm formation in PaWT. On the other hand, the effects of SaEVs on the production of lipid A and LPS core and biofilm formation in PaΔpslE were abolished. Invasion of PaWT and PaΔpslE into HaCaT human epithelial cells was not significantly different and the effect of SaEVs on these bacterial cell invasions was not found. However, the uptake of SaEV-treated PaWT by macrophages significantly reduced compared to nontreated PaWT, whereas SaEVs did not alter the uptake of PaΔpslE. These results suggest that PslE is required for SaEV-mediated P. aeruginosa pathogenicity. SaEVs upregulate pslE gene as well as other exopolysaccharide polymerization-related genes, increase LPS production and biofilm formation, and affect the uptake of P. aeruginosa by macrophages.