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Infection and Immunity, July 1999, p. 3625-3630, Vol. 67, No. 7
Departments of
Medicine1 and of Microbiology and
Immunology,3 University of California, San
Francisco, San Francisco, California 94143, and Centre for
Molecular and Cellular Biology, The University of Queensland,
Brisbane, Queensland 4072, Australia2
Received 9 February 1999/Returned for modification 23 March
1999/Accepted 9 April 1999
Type IV pili of the opportunistic pathogen Pseudomonas
aeruginosa mediate twitching motility and act as receptors for
bacteriophage infection. They are also important bacterial adhesins,
and nonpiliated mutants of P. aeruginosa 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 P. aeruginosa 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 pilT and pilU retain surface
pili but have lost twitching motility. In three different epithelial
cell lines, pilT or pilU mutants of the strain
PAK caused less cytotoxicity than the wild-type strain but more than
isogenic, nonpiliated pilA or rpoN mutants. The
pilT and pilU mutants also showed reduced association with these same epithelial cell lines compared both to the
wild type, and surprisingly, to a pilA mutant. In a mouse model of acute pneumonia, the pilT and pilU
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.
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Pseudomonas aeruginosa Gene Products
PilT and PilU Are Required for Cytotoxicity In Vitro and Virulence in
a Mouse Model of Acute Pneumonia


*
Corresponding author. Mailing address: Division of
Infectious Disease, Box 0654, University of California, San Francisco, CA 94143-0654. Phone: (415) 476-7355. Fax: (415) 476-9364. E-mail: Jengel{at}medicine.ucsf.edu.
Present address: Department of Bacteriology, University of
Wisconsin, Madison, Madison, WI 53706.
Present address: Department of Microbiology and Immunology,
Northwestern University, Chicago, IL 60611.
§
Present address: Department of Obstetrics and Gynecology,
University of California, San Francisco, San Francisco, CA 94143.
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