930. Characterization of a Virulence Factor in the Mechanisms of Shigella Pathogenesis
Session: Poster Abstract Session: Bacterial Pathogenesis
Saturday, October 22, 2011
Room: Poster Hall B1
Background: Gram-negative bacteria utilize the type III secretion system to inject “effector” proteins directly into host cells.  These virulence factors are critical for the lifecycles of many human pathogens and are therefore potential targets in the development of new tools to combat infectious diseases.  VirA and EspG are related effectors from Shigella species and Enterohemorrhagic E. coli, respectively, that are important for virulence but have unknown biochemical functions.  We’ve recently begun to unravel the mechanisms of EspG and used this knowledge to investigate VirA.  We applied our findings to explore the pathogenesis of other intracellular pathogens.

Methods: We analyzed the crystal structures of VirA and EspG and compared their biochemical activities.  A membrane trafficking assay was used to test the role of VirA and EspG in the host secretory pathway.  Microinjection was used to visualize cellular phenotypes.  A mammalian cell culture model was utilized to test the role of VirA in Shigella infection.  Other intracellular pathogens were tested in infection models for comparison.

Results: Our structural analysis revealed several differences to suggest that VirA and EspG have different molecular mechanisms.  Additionally, binding assays revealed potentially unique host targets.  Both effectors inhibited the host secretory pathway and disrupted the Golgi apparatus.  Shigella infection resulted in Golgi disruption, and infection with a virA knockout strain resulted in a similar pattern of Golgi dissolution during infection.  Infection with other intracellular pathogens resulted in no deleterious effects on Golgi morphology.

Conclusion: VirA and EspG have different molecular mechanisms and unique host targets.  However, they both inhibit endomembrane trafficking and disrupt the Golgi and may therefore share common cellular outcomes.  We report a novel phenotype of Golgi disruption during Shigella infection.  VirA was not required for Golgi disruption but may be acting in concert with other unknown virulence factors during Shigella infection.  Golgi disruption is unique to Shigella infection, as other intracellular pathogens did not disrupt the Golgi during infection.

Subject Category: B. Bacterial pathogenesis, studies in animal models, molecular pathogenicity

Thomas G. Fox, MD1, Andrey Selyunin2 and Neal M. Alto, PhD2, (1)Pediatric Infectious Diseases, University of Texas Southwestern, Dallas, TX, (2)Microbiology, University of Texas Southwestern, Dallas, TX


T. G. Fox, None

A. Selyunin, None

N. M. Alto, None

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.