Co-evolution with Staphylococcus aureus leads to lipopolysaccharide alterations in Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Infectious Diseases
• Genomics

Background:

• Bacterial co-colonization in cystic fibrosis (CF) airways involves complex interactions influencing infection outcomes.
• Staphylococcus aureus dominates early CF infections, with Pseudomonas aeruginosa becoming predominant later.

Purpose of the Study:

• To investigate adaptive evolution of P. aeruginosa in response to S. aureus.
• To determine if P. aeruginosa adaptations are specific responses to S. aureus or general environmental responses.

Main Methods:

• Evolving P. aeruginosa populations for 150 generations in the presence and absence of S. aureus.
• Whole-genome sequencing of evolved P. aeruginosa populations and comparison to the ancestor strain.

Main Results:

• Mutations in the Wsp signaling system were found in both conditions, likely due to low oxygen.
• Mutations in lipopolysaccharide (LPS) biosynthesis occurred exclusively in co-cultures with S. aureus, conferring a fitness gain.
• LPS mutations increased resistance to beta-lactam antibiotics and were observed in clinical CF isolates.

Conclusions:

• P. aeruginosa LPS mutations are a direct result of S. aureus-imposed selection in vitro.
• Wsp and LPS mutations found in evolved strains are also present in clinical CF isolates, highlighting their relevance.
• Understanding these interactions is crucial for managing chronic CF lung infections.