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Journal of Clinical Microbiology, February 2004, p. 554-562, Vol. 42, No. 2
0095-1137/04/$08.00+0     DOI: 10.1128/JCM.42.2.554-562.2004
Copyright © 2004, American Society of Microbiology. All Rights Reserved.

Characterization of Cell-to-Cell Signaling-Deficient Pseudomonas aeruginosa Strains Colonizing Intubated Patients

Valérie Dénervaud,¹ Patrick TuQuoc,² Dominique Blanc,³ Sabine Favre-Bonté,^2, Viji Krishnapillai,¹ Cornelia Reimmann,¹ Dieter Haas,¹ and Christian van Delden^2*

Institut de Microbiologie Fondamentale, Université de Lausanne, CH-1015 Lausanne,¹ Division des Maladies Infectieuses, Hôpital Universitaire de Genève, CH-1211 Geneva 14,² Division Autonome de Médecine Préventive, Centre Hospitalier Vaudois, CH-1011 Lausanne, Switzerland³

Received 14 May 2003/ Returned for modification 16 July 2003/ Accepted 29 October 2003

Cell-to-cell signaling involving N-acyl-homoserine lactone compounds termed autoinducers (AIs) is instrumental to virulence factor production and biofilm development by Pseudomonas aeruginosa. In order to determine the importance of cell-to-cell signaling during the colonization of mechanically ventilated patients, we collected 442 P. aeruginosa pulmonary 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 distinct P. aeruginosa strains. Six of these strains produced AIs [N-butanoyl-homoserine lactone or N-(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 the lasR and rhlR genes, which encode the N-acyl-homoserine lactone-dependent transcriptional regulators LasR and RhlR, respectively. The third of these AI-deficient strains was only mutated in the lasR gene. 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.

Present address: UMR CNRS 5557-Ecologie Microbienne, Université Claude Bernard, Lyon I, France.

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