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J. Bacteriol. doi:10.1128/JB.01839-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Presence or Absence of Lipopolysaccharide O-antigens Affects Type III Secretion by Pseudomonas aeruginosa

Biology Department, California State University, San Francisco, CA 94132, USA; Departments of Anesthesia and Perioperative Care, Medicine, the Cardiovascular Research Institute, University of California, San Francisco, CA94143, U.S.A.

^* To whom correspondence should be addressed. Email: lynchs{at}anesthesia.ucsf.edu.

	Abstract

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 infection. 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 mode of lifestyle (e.g. biofilm to planktonic). Given that LPS exhibits structural plasticity, we hypothesized that presence of LPS lacking O-antigen would facilitate eukaryotic intoxication and that a correlation between 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 in clinical isolates of P. aeruginosa.

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