Abstract
BackgroundSome isolates of the Liverpool cystic fibrosis epidemic strain of Pseudomonas aeruginosa exhibit an unusual virulence-related phenotype, characterized by over-production of quorum sensing-regulated exoproducts such as pyocyanin and LasA protease. Our aim was to determine the prevalence of this unusual phenotype amongst isolates of the epidemic strain, and to study other intraclonal phenotypic and genotypic variations.ResultsThe unusual phenotype was detected in at least one epidemic strain isolate from the majority of cystic fibrosis patients tested, and can be retained for up to seven years during chronic infection. Multiple sequential isolates of the epidemic strain taken from six patients over a period of up to nine years exhibited a wide range of phenotypes, including different antimicrobial susceptibilities. Our data suggest that each sputum sample contains a mixture of phenotypes and genotypes within the epidemic strain population, including within colony morphotypes. Many isolates exhibit premature (during early rather than late exponential growth) and over-production of pyocyanin, which has a number of toxic effects directly relevant to cystic fibrosis.ConclusionThe widespread occurrence of this unusual phenotype suggests that it may play an important role in the success of the epidemic strain.
Highlights
Some isolates of the Liverpool cystic fibrosis epidemic strain of Pseudomonas aeruginosa exhibit an unusual virulence-related phenotype, characterized by over-production of quorum sensing-regulated exoproducts such as pyocyanin and LasA protease
Efficacy of a simple Luria broth test for pyocyanin production In order to test the efficacy of a simple screening procedure for pyocyanin production by strains of P. aeruginosa, the amount of pyocyanin in culture supernatants after overnight growth was quantified by measuring the A695 value for 10 environmental strains, 10 strains associated with bacterial keratitis, 29 non-Liverpool Epidemic Strain (LES) cystic fibrosis (CF) and 48 LES isolates (Figure 1)
Prevalence of the OP phenotype A total of 34 non-LES and 55 LES isolates of P. aeruginosa were screened for over-production of pigment by using the simple broth test
Summary
Some isolates of the Liverpool cystic fibrosis epidemic strain of Pseudomonas aeruginosa exhibit an unusual virulence-related phenotype, characterized by over-production of quorum sensing-regulated exoproducts such as pyocyanin and LasA protease. Our aim was to determine the prevalence of this unusual phenotype amongst isolates of the epidemic strain, and to study other intraclonal phenotypic and genotypic variations. CF patients suffer decline in lung function associated with periodic exacerbations triggered by bacterial products. The most widespread CF pathogen is Pseudomonas aeruginosa, which causes infections that, once established, are impossible to eradicate. The blue, redox-active phenazine pyocyanin is secreted by P. aeruginosa under the control of its cell-density-dependent quorum sensing (QS) system [1]. Pyocyanin and its precursor phenazine-1-carboxylic acid (PCA) have a number of toxic effects relevant to CF [2,3].
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