Persistence of large P. aeruginosa aggregates despite reduced airway burden in people with cystic fibrosis on CFTR modulator therapy.

BACKGROUND

Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies improve lung function and reduce airway bacterial burden in people with cystic fibrosis (pwCF); however, chronic Pseudomonas aeruginosa infection can persist and recrudesce. This persistence may be mediated by bacterial aggregation, a phenotype associated with antibiotic tolerance and immune evasion that is not routinely assessed in clinical practice. In this study, we evaluated the impact of CFTR modulation on P. aeruginosa burden and aggregation in sputum from pwCF.

METHODS

PwCF with chronic P. aeruginosa infection were enrolled at three Canadian CF centers (2022-2025). Sputum samples were processed using the Microbial Identification after Passive CLARITY Technique (MiPACT), followed by fluorescence in situ hybridization and confocal microscopy. Image analyses quantified P. aeruginosa biovolume and aggregate number, maximum size and size distribution. Mixed-effects models assessed longitudinal and cross-sectional differences by modulator status.

RESULTS

Forty-two participants contributed 181 samples; 27 received modulators. Longitudinally, modulator therapy reduced P. aeruginosa biovolume (p = 0.01) and aggregate number (p = 0.04), with no significant changes observed in untreated individuals. Cross-sectional analyses showed no differences in biovolume and aggregate number by treatment status. Maximum aggregate size and the proportion of large aggregates were also comparable between groups with approximately 20% of P. aeruginosa persisting as large aggregates in both groups.

CONCLUSIONS

CFTR modulators reduce P. aeruginosa density but not aggregation. Persistent aggregates may represent structurally resilient communities contributing to chronic infection, highlighting aggregation as a potential adjunctive therapeutic target.