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Infection and Immunity, March 2005, p. 1695-1705, Vol. 73, No. 3
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.3.1695-1705.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Activities of Pseudomonas aeruginosa Effectors Secreted by the Type III Secretion System In Vitro and during Infection

Vincent T. Lee,1 Roger S. Smith,1 Burkhard Tümmler,2 and Stephen Lory1*

Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts,1 Department of Pediatric Pneumology, Hannover Medical School, 30265 Hannover, Germany2

Received 12 July 2004/ Returned for modification 6 October 2004/ Accepted 18 November 2004

Pseudomonas aeruginosa utilizes a number of distinct pathways to secrete proteins that play various roles during infection. These include the type II secretion system, which is responsible for the secretion of the majority of exoproducts into the surrounding environment, including toxins and degradative enzymes. In contrast, the type III secretion system mediates the delivery of protein effectors directly into the cytoplasm of the host cell. Using tissue culture assays and a mouse acute-pneumonia model, we have determined the contribution of each of the type III effectors during infection. In strain PAK, ExoS is the major cytotoxin required for colonization and dissemination during infection. ExoT confers protection of tissue culture cells from type III-dependent lysis, while ExoY seemed to have little effect on cytotoxicity. ExoU is over 100-fold more cytotoxic than ExoS. The cytotoxicity of type II secretion was determined following deletion of the genes for the more toxic type III secretion system. The participation of these secretion systems during lifelong colonization of cystic fibrosis (CF) patients is unclear. By comparing clonal strains from the same patient isolated at the initial onset of P. aeruginosa infection and more than a decade later, after chronic colonization has been established, we show that initial strains are more cytotoxic than chronic strains that have evolved to reduce type III secretion. Constitutive expression of genes for the type III secretion system restored ExoS secretion but did not always reestablish cytotoxicity, suggesting that CF strains accumulate a number of mutations to reduce bacterial toxicity to the host.

* Corresponding author. Mailing address. Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115. Phone: (617) 432-5099. Fax: (617) 738-7664. E-mail: stephen_lory{at}hms.harvard.edu.

Editor: V. J. DiRita

Infection and Immunity, March 2005, p. 1695-1705, Vol. 73, No. 3
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.3.1695-1705.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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