Email updates

Keep up to date with the latest news and content from BMC Microbiology and BioMed Central.

Open Access Highly Accessed Research article

A galU mutant of francisella tularensis is attenuated for virulence in a murine pulmonary model of tularemia

Himangi R Jayakar12, Jyothi Parvathareddy1, Elizabeth A Fitzpatrick1, Xiaowen R Bina1, James E Bina1, Fabio Re1, Felicia D Emery1 and Mark A Miller1*

Author Affiliations

1 Department of Microbiology, Immunology, and Biochemistry, The University of Tennessee Health Science Center, 858 Madison Avenue, Memphis, Tennessee 38163, USA

2 Department of Immunology and Microbial Sciences, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA

For all author emails, please log on.

BMC Microbiology 2011, 11:179  doi:10.1186/1471-2180-11-179

Published: 5 August 2011

Abstract

Background

A number of studies have revealed that Francisella tularensis (FT) suppresses innate immune responses such as chemokine/cytokine production and neutrophil recruitment in the lungs following pulmonary infection via an unidentified mechanism. The ability of FT to evade early innate immune responses could be a very important virulence mechanism for this highly infectious bacterial pathogen.

Results

Here we describe the characterization of a galU mutant strain of FT live vaccine strain (LVS). We show that the galU mutant was highly attenuated in a murine model of tularemia and elicited more robust innate immune responses than the wild-type (WT) strain. These studies document that the kinetics of chemokine expression and neutrophil recruitment into the lungs of mice challenged with the galU mutant strain are significantly more rapid than observed with WT FT, despite the fact that there were no observed differences in TLR2 or TLR4 signaling or replication/dissemination kinetics during the early stages of infection. We also show that the galU mutant had a hypercytotoxic phenotype and more rapidly induced the production of IL-1β following infection either in vitro or in vivo, indicating that attenuation of the galU mutant strain may be due (in part) to more rapid activation of the inflammasome and/or earlier death of FT infected cells. Furthermore, we show that infection of mice with the galU mutant strain elicits protective immunity to subsequent challenge with WT FT.

Conclusions

Disruption of the galU gene of FTLVS has little (if any) effect on in vivo infectivity, replication, or dissemination characteristics, but is highly attenuating for virulence. The attenuated phenotype of this mutant strain of FT appears to be related to its increased ability to induce innate inflammatory responsiveness, resulting in more rapid recruitment of neutrophils to the lungs following pneumonic infection, and/or to its ability to kill infected cells in an accelerated fashion. These results have identified two potentially important virulence mechanisms used by FT. These findings could also have implications for design of a live attenuated vaccine strain of FT because sublethal infection of mice with the galU mutant strain of FTLVS promoted development of protective immunity to WT FTLVS.