Clinical isolates from chronic wounds reveal strain-specific, alkyl-quinolone- independent, competition in Pseudomonas aeruginosa-Staphylococcus aureus biofilms

Introduction: Chronic wounds are notoriously difficult to treat and are associated with decreased limb function, reduced quality of life, and significant morbidity. Their recurrent nature, despite aggressive antibiotic therapy, is due in part to the presence of polymicrobial biofilms. Pseudomonas aeruginosa and Staphylococcus aureus are two of the most frequently co-isolated pathogens in these infections and are known to form complex biofilms that hinder treatment. Hypothesis:We hypothesised that coexistence and competitive dynamics between P. aeruginosa and S. aureus in chronic wound infections are influenced by strain-specific interactions and may not rely solely on well-characterised inhibitory mechanisms such as 2-alkyl-4-quinolone (AQ) production by P. aeruginosa impacting on S. aureus fitness. Aim: To establish a polymicrobial chronic wound infection model and assess the contribution of AQ signalling and strain specific interactions on coexistence. Methodology: We used a modified chronic wound biofilm (mCWB) model to co-culture matched and mismatched clinical isolate pairs of P. aeruginosa and S. aureus, collected from two different chronic wound patients. Viable bacterial counts (CFUs) were quantified over an 8-day period. AQ production by each P. aeruginosa strain was quantified using liquid chromatography-mass spectrometry (LC-MS/MS). Results: Stable culture of P. aeruginosa strains was achieved but distinct behaviours between each S. aureus strain were seen. One matched clinical isolate pair maintained stable CFU levels of both species throughout the 8-day model, indicating a compatible coexistence. In contrast, mismatched pairs showed early loss of S. aureus viability, and the emergence of small colony variants (SCVs) after 4 days not seen in matched pair growth. Interestingly, the most competitive P. aeruginosa strain exhibited undetectable levels of all AQs tested, indicating that its dominance was not due to AQ-mediated antagonism, as has previously been described. Conclusions: Our findings demonstrate that stable dual-species biofilm formation in chronic wounds is strain-dependent and that P. aeruginosa can impact on S. aureus fitness through AQ-independent mechanisms. These results highlight the importance of using clinical isolates in biofilm research and caution against generalising findings from laboratory strains to complex clinical Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation