Examining the Distribution of the Extracellular Polymeric Substances in the Biofilms of the Liverpool Epidemic Strain of Pseudomonas aeruginosa

The Liverpool Epidemic Strain (LES) of Pseudomonas aeruginosa is responsible for causing antibiotic resistant, transmissible infections in individuals with cystic fibrosis. The biofilm lifestyle, which has been well characterized in P. aeruginosa, is thought to contribute to the enhanced ability of isolates of this strain to resist drug therapy and persist in the lung environment. The extracellular polymeric substances (EPS) produced by biofilm cells have been implicated in biofilm mediated drug resistance, although their abundance, localization and response to antibiotic treatment has not previously been characterized in the LES. In this study the predominant EPS components, extracellular DNA (eDNA) and secreted polysaccharides, were quantified using fluorescent staining and confocal microscopy in biofilms of eight LES isolates grown in flow cells. The LES isolates formed biofilms that were phenotypically distinct from one another and the EPS components do not follow the same localization patterns as the laboratory standard P. aeruginosa PAO1. When treated with aztreonam, LESlike4 exhibited an increase in EPS components that was not seen in LES400 or in PAO1. While these specific isolates share many of the same genes, each has a unique profile of SNPs and genetic elements that are likely responsible for the observed phenotypic diversity. A better understanding of the genotypic and phenotypic diversity of the LES isolates is necessary for the development of therapies able to eradicate the chronic infections they cause.