<i>Pseudomonas aeruginosa</i> Gene Products PilT and PilU Are Required for Cytotoxicity In Vitro and Virulence in a Mouse Model of Acute Pneumonia

<jats:title>ABSTRACT</jats:title> <jats:p> Type IV pili of the opportunistic pathogen <jats:italic>Pseudomonas aeruginosa</jats:italic> mediate twitching motility and act as receptors for bacteriophage infection. They are also important bacterial adhesins, and nonpiliated mutants of <jats:italic>P. aeruginosa</jats:italic> have been shown to cause less epithelial cell damage in vitro and have decreased virulence in animal models. This finding raises the question as to whether the reduction in cytotoxicity and virulence of nonpiliated <jats:italic>P. aeruginosa</jats:italic> mutants are primarily due to defects in cell adhesion or loss of twitching motility, or both. This work describes the role of PilT and PilU, putative nucleotide-binding proteins involved in pili function, in mediating epithelial cell injury in vitro and virulence in vivo. Mutants of <jats:italic>pilT</jats:italic> and <jats:italic>pilU</jats:italic> retain surface pili but have lost twitching motility. In three different epithelial cell lines, <jats:italic>pilT</jats:italic> or <jats:italic>pilU</jats:italic> mutants of the strain PAK caused less cytotoxicity than the wild-type strain but more than isogenic, nonpiliated <jats:italic>pilA</jats:italic> or <jats:italic>rpoN</jats:italic> mutants. The <jats:italic>pilT</jats:italic> and <jats:italic>pilU</jats:italic> mutants also showed reduced association with these same epithelial cell lines compared both to the wild type, and surprisingly, to a <jats:italic>pilA</jats:italic> mutant. In a mouse model of acute pneumonia, the <jats:italic>pilT</jats:italic> and <jats:italic>pilU</jats:italic> mutants showed decreased colonization of the liver but not of the lung relative to the parental strain, though they exhibited no change in the ability to cause mortality. These results demonstrate that pilus function mediated by PilT and PilU is required for in vitro adherence and cytotoxicity toward epithelial cells and is important in virulence in vivo. </jats:p>