Pseudomonas aeruginosacontracts mucus to form biofilms in tissue-engineered human airways

The opportunistic pathogenPseudomonas aeruginosacauses antibiotic-recalcitrant pneumonia by forming biofilms in the respiratory tract. Despite extensivein vitroexperimentation, howP. aeruginosaforms biofilms at the airway mucosa is unresolved. To investigate the process of biofilm formation in realistic conditions, we developed AirGels: 3D, optically-accessible tissue-engineered human lung models that emulate the airway mucosal environment. AirGels recapitulate important factors that mediate host-pathogen interactions including mucus secretion, flow and air-liquid interface, while accommodating high resolution live microscopy. With AirGels, we investigated the contributions of mucus toP. aeruginosabiofilm biogenesis inin vivo-like conditions. We found thatP. aeruginosaforms mucus-associated biofilms within hours by contracting luminal mucus early during colonization. Mucus contractions facilitates aggregation, thereby nucleating biofilms. We show thatP. aeruginosaactively contracts mucus using retractile filaments called type IV pili. Our results therefore suggest that, while protecting epithelia, mucus constitutes a breeding ground for biofilms.