Infection dynamics and virulence potential of clinical Pseudomonas aeruginosa isolates in a human airway epithelium model system

Persistent bacterial infections constitute an increasing health problem, which is often associated with antibiotic resistance. However, investigations of chronic lung inflammation and persistent infections with Pseudomonas aeruginosa in people with cystic fibrosis (pwCF) show that treatment failures may instead be rooted in host-microbe interactions developing after bacterial colonization of the CF airways. Using a laboratory infection model based on human airway epithelial tissues, cultured in an Air-Liquid Interface (ALI) system, we simulated the infection process of various P. aeruginosa strains to investigate the colonisation dynamics and the virulence potential during infection of nasal epithelial cultures from both non-CF and CF donors in addition to an immortalized bronchial cell line, BCi-NS1.1. Infections by P. aeruginosa reference strains and clinical isolates from pwCF were employed. While reference and patients' early strains exhibited high virulence and increased epithelial disruption, clinically adapted strains showed reduced virulence potential and limited epithelial damage regardless of the host cell type or clonal lineage. Dual RNA-seq analysis revealed that colonization of ALI cultures with virulent PAO1 significantly upregulated inflammatory pathways in host cells, an effect that was dampened in the less virulent pscC mutant strain lacking the type III secretion system. Simultaneously, while bacterial gene expression was similar in wild-type and BCi-NS1.1 cultures, in CF cells, the pscC strain showed dysregulation of genes involved in iron starvation, respiration, and quorum sensing pathways. Altogether, our results summarize the infection dynamics in the ALI model system and in pwCF, and provide a snapshot of the interplay between the airway epithelium and P. aeruginosa.