Unpublished epidemiologic study results indicate that only certain Pseudomonas aeruginosa strains, marked by specific alleles of the oprD porine protein encoding gene are able to colonize cystic fibrosis patients. Construction of different OprD mutants and infection with these bacterial strains of different in vitro airway epithelial cell line cultures willenable to elucidate the role of this porin in internationalisation of this bacterium in airway epithelial cells as a first step towards persistent colonisation of the cystic fibrosis lung.