Characterization of Cell-to-Cell Signaling-DeficientPseudomonas aeruginosaStrains Colonizing Intubated Patients

Abstract

ABSTRACTCell-to-cell signaling involvingN-acyl-homoserine lactone compounds termed autoinducers (AIs) is instrumental to virulence factor production and biofilm development byPseudomonas aeruginosa. In order to determine the importance of cell-to-cell signaling during the colonization of mechanically ventilated patients, we collected 442P. aeruginosapulmonary isolates from 13 patients. Phenotypic characterization showed that 81% of these isolates produced the AI-dependent virulence factors elastase, protease, and rhamnolipids. We identified nine genotypically distinctP. aeruginosastrains. Six of these strains produced AIs [N-butanoyl-homoserine lactone orN-(3-oxo-dodecanoyl)-homoserine lactone] and extracellular virulence factors (elastase, total exoprotease, rhamnolipid, hydrogen cyanide, or pyocyanin) in vitro. Three of the nine strains were defective in the production of both AIs and extracellular virulence factors. Two of these strains had mutational defects in both thelasRandrhlRgenes, which encode theN-acyl-homoserine lactone-dependent transcriptional regulators LasR and RhlR, respectively. The third of these AI-deficient strains was only mutated in thelasRgene. Our observations suggest that most, but not all, strains colonizing intubated patients are able to produce virulence factors and that mutations affecting the cell-to-cell signaling circuit are preferentially located in the transcriptional regulator genes.