The Effect of Human Airway Lung Secretions on Pseudomonas aeruginosa Twitching Motility

Background: Pseudomonas aeruginosa irreversibly colonizes the lungs of and is the leading cause of death in people with cystic fibrosis (CF). P. aeruginosa has two main modes of motility – flagella-mediated swimming through fluid and type IV pili-mediated twitching on a surface – and motility is associated with increased virulence.  Twitching motility is likely critical for the spread and colonization of P. aeruginosa in the CF lung.  Because P. aeruginosa is prevented from colonizing the non-CF lung, we proposed that non-CF lung secretions would inhibit the twitching motility of P. aeruginosawhereas CF-lung secretions would not, thus promoting permanent colonization of the CF lung. Methods:  We established a functional, microscopic, pseudo-quantitative twitching assay for the PA14 strain of P. aeruginosa and harvested apical secretions from a monolayer of wild-type and CF-like Calu-3 cells. PA14 was pre-treated with the airway secretions before twitching analysis Results: Twitching motility was consistently observed on the edges of PA14 growth at 37^oC. Addition of non-CF airway secretions did not significantly inhibit PA14 twitching, but did cause consistent anomalous bacterial movement in limited areas of the field of view. Conclusions: Normal airway secretions did not globally inhibit P. aeruginosa twitching motility, but did induce some aberrant local movements that may reflect interference with quorum sensing or other inter-bacterial communication.