Abstract
Background: On reaching adulthood, the lungs of people with cystic fibrosis (CF) harbour P. aeruginosa infection, with this organism having apparently eliminated earlier S. aureus. Chronic, progressive respiratory disease is the main cause of death in CF.
Aims and Objectives: We employed several clinical isolates of P. aeruginosa from CF airways in order to examine virulence factor production and ability to outcompete S. aureus. In addition, using in vitro models of human airways, we addressed whether these pathogens can adhere more readily to CF cells.
Methods: Crystal violet staining was used to assess biofilm production, skimmed milk agar plates were used to reveal protease activity and pyocyanin production was quantified via chloroform extraction. Growth competition was measured in planktonic culture. Bronchial epithelial cells were grown to confluence before submerged monolayers were infected with S. aureus for 2 hours, prior to determining adherent bacterial numbers.
Results: Whilst virulence varied between the different clinical isolates of P. aeruginosa, they all outcompeted S. aureus. However, S. aureus adhered equally to submerged CF and non-CF cells and we are currently using differentiated cultures to determine whether bacteria adhere to the mucus, as previously suggested [Ulrich M, et al. Am J Respir Cell Mol Biol. 1998;19:83-91].
Conclusion: P. aeruginosa dominance over S. aureus cannot be attributed to a single virulence factor. Conditions in the CF lung alter virulence, with different clinical isolates releasing different quantities of biofilm, pyocyanin and protease but this still does not affect the ability of P. aeruginosa to outcompete S. aureus.
- Copyright ©the authors 2016
