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Journal of Bacteriology, March 2007, p. 2203-2209, Vol. 189, No. 6
0021-9193/07/$08.00+0     doi:10.1128/JB.01839-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Presence or Absence of Lipopolysaccharide O Antigens Affects Type III Secretion by Pseudomonas aeruginosa{triangledown}

D. K. Augustin,1,2 Y. Song,2 M. S. Baek,2 Y. Sawa,2 G. Singh,2 B. Taylor,2 A. Rubio-Mills,2 J. L. Flanagan,2 J. P. Wiener-Kronish,2,3,4 and S. V. Lynch2*

Biology Department, California State University, San Francisco, California 94132,1 Departments of Anesthesia and Perioperative Care,2 Medicine,3 the Cardiovascular Research Institute, University of California, San Francisco, California 941434

Received 7 December 2006/ Accepted 21 December 2006

Pseudomonas aeruginosa is one of the major causative agents of mortality and morbidity in hospitalized patients due to a multiplicity of virulence factors associated with both chronic and acute infections. Acute P. aeruginosa infection is primarily mediated by planktonic bacteria expressing the type III secretion system (TTSS), a surface-attached needle-like complex that injects cytotoxins directly into eukaryotic cells, causing cellular damage. Lipopolysaccharide (LPS) is the principal surface-associated virulence factor of P. aeruginosa. This molecule is known to undergo structural modification (primarily alterations in the A- and B-band O antigen) in response to changes in the mode of life (e.g., from biofilm to planktonic). Given that LPS exhibits structural plasticity, we hypothesized that the presence of LPS lacking O antigen would facilitate eukaryotic intoxication and that a correlation between the LPS O-antigen serotype and TTSS-mediated cytotoxicity would exist. Therefore, strain PAO1 (A+ B+ O-antigen serotype) and isogenic mutants with specific O-antigen defects (A+ B, A B+, and A B) were examined for TTSS expression and cytotoxicity. A strong association existed in vitro between the absence of the large, structured B-band O antigen and increased cytotoxicity of these strains. In vivo, all three LPS mutant strains demonstrated significantly increased lung injury compared to PAO1. Clinical strains lacking the B-band O antigen also demonstrated increased TTSS secretion. These results suggest the existence of a cooperative association between LPS O-antigen structure and the TTSS in both laboratory and clinical isolates of P. aeruginosa.


* Corresponding author. Mailing address: Departments of Anesthesia and Perioperative Care, University of California, San Francisco, CA 94143. Phone: (415) 476-6784. Fax: (415) 476-8841. E-mail: lynchs{at}anesthesia.ucsf.edu.

{triangledown} Published ahead of print on 5 January 2007.


Journal of Bacteriology, March 2007, p. 2203-2209, Vol. 189, No. 6
0021-9193/07/$08.00+0     doi:10.1128/JB.01839-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.




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