Components of cystic fibrosis sputum influence the virulence of Pseudomonas aeruginosa

Date

2013-08

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Abstract

The accumulation of thick stagnant mucus provides a suitable environment for the growth of Pseudomonas aeruginosa within the lung alveoli of Cystic fibrosis (CF) patients. These infections cause significant lung damage, leading to respiratory failure and death. In different infection sites, bacteria exist in special structures termed biofilms, which protect them from the host immune response. In the first phase of this study, we showed that in a synthetic mucus medium that resembles CF alveolar mucus, P. aeruginosa failed to form biofilms but instead produced free floating aggregates which we termed biofilm-like structures (BLS). The formation ofBLS is influenced by the amount of DNA, mucin and the level of environmental oxygen (E02). A defect in the rhll and rhlR quorum sensing genes (QS) affected the formation ofBLS. When coinoculated with Staphylococcus aureus, P. aeruginosa formed dual BLS, but gradually eliminated S. aureus from the structures. In the second phase, we identified the mucus component that inhibits P. aeruginosa biofilm development. Mucin significantly enhanced twitching motility and decreased P. aeruginosa biofilm formation in a concentration dependent manner. Mucin enhanced transcription of pi/A, which encodes pilin protein as well as surface display of pilin protein. Mucin failed to enhance twitching motility in P. aeruginosa mutants defective inpilA, pilR, rpoN,fimV, and several genes of the pilin biogenesis operons pilGHl/pilJK-chpA-D. In the third phase, we developed a new synthetic mucus medium, Cystic fibrosisLubbock/ Mucin medium (CF-LIM) that contains all components of CF mucus (including salts, amino acids, DNA, lecithin, and mucin) at concentrations that mimic their levels in CF mucus. Although CF-LIM supported the growth of P. aeruginosa, the expression of different iron-regulated genes was significantly reduced. This effect is due to the presence of a sufficient amount of free iron within mucin. In contrast to mucin, lecithin enhanced the expression of iron-regulated genes, but DNA had no effect. In conclusion, our study indicates that components of alveolar mucus influence the pathogenesis of P. aeruginosa chronic lung infections in CF patients. Manipulations of these components will be critical in defining potential targets for future therapies.

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Keywords

Cystic fibrosis, Pseudomonas aeruginosa, Sputum influence

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