The Effects of Human Airway Secretions on Pseudomonas aeruginosa Biofilm Formation

Background: Pseudomonas aeruginosa causes severe disease in patients with cystic fibrosis (CF), though it rarely causes airway disease in people without CF. The formation of a bacterial biofilm in the CF lung is likely an initial step in colonization and, once formed, the biofilm would largely protect P. aeruginosa from immune clearance and antibiotic treatment.  Human lung secretions typically contain substantial antimicrobial activities, though these are often not present or reduced in CF lung secretions. We hypothesized that non-CF airway secretions would inhibit and/or that CF-airway secretions would promote P. aeruginosabiofilm formation in vitro. Methods: The PAO1 strain of P. aeruginosawas allowed to form biofilms in the presence or absence of apical secretions from wild-type or CF-like Calu-3 cells. Biofilm formation was quantitated using crystal violet staining of the biofilm and measurement of OD in a plate reader. Results:We established a robust, static biofilm assay using PAO1. Addition of wild-type (non-CF) Calu-3 secretions to the bacteria significantly inhibited biofilm formation compared to controls. Conclusions:Wild-type (non-CF) airway secretions inhibit PAO1 static biofilm formation and preliminary findings suggest this inhibition is likely due to a protein or proteins present in the secretion.