Abstract
BACKGROUND: Co-colonization by Pseudomonas aeruginosa and Staphylococcus aureus is frequent in cystic fibrosis patients. Polymicrobial infections involve both detrimental and beneficial interactions between different bacterial species. Such interactions potentially indirectly impact the human host through virulence, antibiosis and immunomodulation. RESULTS: Here we explored the responses triggered by the encounter of these two pathogens to identify early processes that are important for survival when facing a potential competitor. Transcriptional profiles of both bacteria were obtained after 3 h co-culture and compared to the respective mono-culture using RNAseq. Global responses in both bacteria included competition for nitrogen sources, amino acids and increased tRNA levels. Both organisms also induced lysogenic mechanisms related to prophage induction (S. aureus) and R- and F- pyocin synthesis (P. aeruginosa), possibly as a response to stress resulting from nutrient limitation or cell damage. Specific responses in S. aureus included increased expression of de novo and salvation pathways for purine and pyrimidine synthesis, a switch to glucose fermentation, and decreased expression of major virulence factors and global regulators. CONCLUSIONS: Taken together, transcriptomic data indicate that early responses between P. aeruginosa and S. aureus involve competition for resources and metabolic adaptations, rather than the expression of bacteria- or host-directed virulence factors.