92 Increasing virulence, acute phenotypic adaptations and evolving host–pathogen interactions during chronic Burkholderia cepacia complex infection of the cystic fibrosis lung

Objectives We aimed to define the phenotypic and genotypic adaptations that occur in the Burkholderia cepacia complex (BCC) during chronic infection of the cystic fibrosis (CF) lung. Methods We studied a total of 57 BCC isolates from 15 CF patients (2–6 isolates per patient), spanning infection periods ranging from 3 to 14 years. We assessed virulence using the Galleria mellonella model, and phenotypically characterized all isolates to determine how individual traits evolve during infection. Genome sequencing of selected early and late isolates provided insight into the genetic basis of the adaptations, whilst selected isolates were also studied in a murine infection model and in vitro macrophage model. Results Strikingly, during infection of 4 BCC-infected patients, the virulence of longitudinal isolates increased. Those patients were infected with either the B. cenocepacia ET-12 lineage (n = 3) or a B. multivorans outbreak strain (n = 1), both of which are linked with poor clinical outcome. Increasing virulence was uniformly correlated with increased haemolytic activity and decreased biofilm formation, consistent with the emergence of an ‘acute phenotype'. Late isolates displaying heightened virulence also exhibited altered host–pathogen interactions, with delayed clearance from Galleria and/or murine infection models, and reduced uptake by macrophages in vitro. Genome sequencing of isolates revealed evidence of convergent evolution, with comparable phenotypic adaptations arising through distinct genetic mutations. Conclusion BCC adaptation strategies within the CF lung differ from those observed in Pseudomonas aeruginosa , and may contribute to poor clinical outcome.