93* Different genetic adaptation strategies of mucoid and non-mucoid Pseudomonas aeruginosa in the airway of cystic fibrosis patients

Abstract

Pseudomonas aeruginosa is the pathogen most commonly associated with morbidity and mortality in cystic fibrosis (CF). While most CF patients are infected with individual P. aeruginosa strains believed to be environmental in origin, in recent years strains that are transmissible from person to person have been emerging within CF clinics. These epidemic strains are often atypical, many are multi-drug resistant and some possess unusual characteristics such as an increased ability to aerosolise. The microbial factors responsible for these characteristics are not clear. We are using insertion sequences (IS) to investigate these factors, and to study the evolution of these strains. IS are mobile DNA elements possessing only the genes that allow them to move from one genomic site to another. By mapping IS to the genome we can determine genes necessary for survival and spread of P. aeruginosa. Intragenic insertion suggests that these particular genes are not crucial for cell survival since their transcription will be interrupted, whereas essential genes should not contain IS. Certain “active” IS can also act as promotors for downstream gene activation. A genome–based study was conducted to compare IS sites in the Liverpool and Manchester epidemic strains (LES and MAN) with those of three non-epidemic strains. All five strains had multiple IS. However, unlike the genomes of the nonepidemic strains, which had IS spread throughout the genome, MAN and LES had a propensity for IS clustering. The genes immediately downstream of two active IS in LES and MAN were determined and included homologs of glycosyl transferases and of genes involved in oxidoreductase activity. Supported by: The CF Trust, UK.