Extracellular vesicles of Pseudomonas aeruginosa downregulate pyruvate fermentation enzymes and inhibit the initial growth of Staphylococcus aureus

Staphylococcus aureus and Pseudomonas aeruginosa are well-known opportunistic pathogens that frequently coexist in chronic wounds and cystic fibrosis. The exoproducts of P. aeruginosa have been shown to affect the growth and pathogenicity of S. aureus, but the detailed mechanisms are not well understood. In this study, we investigated the effect of extracellular vesicles from P. aeruginosa (PaEVs) on the growth of S. aureus. We found that PaEVs inhibited the S. aureus growth independently of iron chelation and showed no bactericidal activity. This growth inhibitory effect was also observed with methicillin-resistant S. aureus but not with Acinetobacter baumannii, Enterococcus faecalis, S. Typhimurium, E. coli, Listeria monocytogenes, or Candida albicans, suggesting that the growth inhibitory effect of PaEVs is highly specific for S. aureus. To better understand the detailed mechanism, the difference in protein production of S. aureus between PaEV-treated and non-treated groups was further analyzed. The results revealed that lactate dehydrogenase 2 and formate acetyltransferase enzymes in the pyruvate fermentation pathway were significantly reduced after PaEV treatment. Likewise, the expression of ldh2 gene for lactate dehydrogenase 2 and pflB gene for formate acetyltransferase in S. aureus was reduced by PaEV treatment. In addition, this inhibitory effect of PaEVs was abolished by supplementation with pyruvate or oxygen. These results suggest that PaEVs inhibit the growth of S. aureus by suppressing the pyruvate fermentation pathway. This study reported a mechanism of PaEVs in inhibiting S. aureus growth which may be important for better management of S. aureus and P. aeruginosa co-infections.