The effect of Staphylococcus aureus on the persistence of Pseudomonas aeruginosa due to aggregation in cystic fibrosis airway infections.

Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) co-infection has been associated with worse clinical outcomes in people with cystic fibrosis (pwCF); however, the nature of their interaction is poorly understood. This was a 3-year prospective study of pwCF with chronic Pa infection. Pa, Sa,and staphylococcal protein A (SpA) were visualized by confocal microscopy in sputum samples obtained at baseline, exacerbation, after antibiotic treatment,and recovery. Forty-five participants were enrolled. At exacerbation, Pa biovolume and aggregate number increased in children, as well as geospatial distancing of Pa from Sa. With IV antibiotics, Pa (0.5-20 μm diameter) decreased significantly more than large Pa aggregates (>20 μm). Increasing sputum SpA concentrations were correlated with higher Pa biovolume in children (p = 0.04, r = 0.54). Within CF airways, Pa and Sa occupy spatially distinct niches but may interact through SpA production in children. Large Pa aggregates persisted despite antibiotics, indicating sustained infection.