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Infection and Immunity, September 2007, p. 4298-4304, Vol. 75, No. 9
0019-9567/07/$08.00+0     doi:10.1128/IAI.00285-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Fate of a Burkholderia pseudomallei Lipopolysaccharide Mutant in the Mouse Macrophage Cell Line RAW 264.7: Possible Role for the O-Antigenic Polysaccharide Moiety of Lipopolysaccharide in Internalization and Intracellular Survival

Department of Microbiology, Faculty of Science, Mahidol University, Bangkok, Thailand,¹ Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, Alberta, Canada²

Received 21 February 2007/ Returned for modification 30 March 2007/ Accepted 6 June 2007

Burkholderia pseudomallei is a facultative intracellular gram-negative bacterium that can survive and multiply inside macrophages. One of the mechanisms by which B. pseudomallei escapes macrophage killing is by interfering with the expression of inducible nitric oxide synthase (iNOS). However, the bacterial components that modulate antimicrobial activity of the macrophage have not been fully elucidated. In the present study, we demonstrated that B. pseudomallei strain SRM117, a lipopolysaccharide (LPS) mutant that lacks the O-antigenic polysaccharide moiety, was more susceptible to macrophage killing during the early phase of infection than the parental wild-type strain (1026b). Unlike the wild type, the LPS mutant could readily stimulate Y701-STAT-1 phosphorylation (pY701-STAT-1) and interferon-regulatory factor 1 (IRF-1) expression, both of which are essential transcription factors of iNOS. Neutralizing antibody against beta interferon was able to inhibit the phosphorylation of Y701-STAT-1 and the expression of IRF-1 and iNOS, all of which resulted in an increased rate of intracellular replication. These data suggest that the O-antigenic polysaccharide moiety of B. pseudomallei modulates the host cell response, which in turn controls the intracellular fate of B. pseudomallei inside macrophages.

Published ahead of print on 18 June 2007.

Editor: J. B. Bliska