In this study, a pathophysiological link between the acquisition of lipid nutrients and virulence in vivo was established by i) characterizing these two P. aeruginosa fadD genes expressed during lung infection in CF patients, ii) determining that there may be some connection between fad-genes and the expression of certain virulence traits, and iii) showing that mutations in these genes correspond to a deficiency in the ability to replicate in mouse lungs. Here, FADD is linked to cystic fibrosis.