Open Access Research article

Type three secretion system-mediated escape of Burkholderia pseudomallei into the host cytosol is critical for the activation of NFκB

Boon Eng Teh1, Christopher Todd French2, Yahua Chen1, Isabelle Gek Joo Chen1, Ting-Hsiang Wu34, Enrico Sagullo3, Pei-Yu Chiou45, Michael A Teitell35678, Jeff F Miller258 and Yunn-Hwen Gan19*

Author Affiliations

1 Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597, Singapore

2 Department of Microbiology, Immunology and Molecular Genetics, Los Angeles, CA 90095, USA

3 Department of Pathology and Laboratory Medicine, Los Angeles, CA 90095, USA

4 Department of Mechanical and Aerospace Engineering, Los Angeles, CA 90095, USA

5 California NanoSystems Institute, Los Angeles, CA 90095, USA

6 Broad Stem Cell Research Center, Los Angeles, CA 90095, USA

7 Jonsson Comprehensive Cancer Center, The University of California Los Angeles, Los Angeles, CA 90095, USA

8 Molecular Biology Institute, The University of California Los Angeles, Los Angeles, CA 90095, USA

9 Immunology Program, National University of Singapore, Singapore 117597, Singapore

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BMC Microbiology 2014, 14:115  doi:10.1186/1471-2180-14-115

Published: 6 May 2014

Abstract

Background

Burkholderia pseudomallei is the causative agent of melioidosis, a potentially fatal disease endemic in Southeast Asia and Northern Australia. This Gram-negative pathogen possesses numerous virulence factors including three “injection type” type three secretion systems (T3SSs). B. pseudomallei has been shown to activate NFκB in HEK293T cells in a Toll-like receptor and MyD88 independent manner that requires T3SS gene cluster 3 (T3SS3 or T3SSBsa). However, the mechanism of how T3SS3 contributes to NFκB activation is unknown.

Results

Known T3SS3 effectors are not responsible for NFκB activation. Furthermore, T3SS3-null mutants are able to activate NFκB almost to the same extent as wildtype bacteria at late time points of infection, corresponding to delayed escape into the cytosol. NFκB activation also occurs when bacteria are delivered directly into the cytosol by photothermal nanoblade injection.

Conclusions

T3SS3 does not directly activate NFκB but facilitates bacterial escape into the cytosol where the host is able to sense the presence of the pathogen through cytosolic sensors leading to NFκB activation.