Quorum-sensing signals indicate that cystic fibrosis lungs are infected with bacterial biofilms

The bacterium Pseudomonas aeruginosa permanently colonizes cystic fibrosis lungs despite aggressive antibiotic treatment(1-3). This suggests that P. a eruginosa might exist as biofilms-structured communities of bacteria encase d in a self-produced polymeric matrix-in the cystic fibrosis lung(1,4). Con sistent with this hypothesis, microscopy of cystic fibrosis sputum shows th at P. aeruginosa are in biofilm-like structures. P. aeruginosa uses extrace llular quorum-sensing signals (extracellular chemical signals that cue cell -density-dependent gene expression) to coordinate biofilm formation(5). Her e we found that cystic fibrosis sputum produces the two principal P. aerugi nosa quorum-sensing signals; however, the relative abundance of these signa ls was opposite to that of the standard P. aeruginosa strain PAO1 in labora tory broth culture. When P. aeruginosa sputum isolates were grown in broth, some showed quorum-sensing signal ratios like those of the laboratory stra in. When we grew these isolates and PAO1 in a laboratory biofilm model, the signal ratios were like those in cystic fibrosis sputum. Our data support the hypothesis that P. aeruginosa are in a biofilm in cystic fibrosis sputu m. Moreover, quorum-sensing signal profiling of specific P. aeruginosa stra ins may serve as a biomarker in screens to identify agents that interfere w ith biofilm development.