Characterization of VIBRIO Parahaemolyticus-Induced Intestinal Inflammation in the Mouse

The Gram-negative marine bacterium Vibrio parahaemolyticus is a leading cause of gastroenteritis from the consumption of contaminated seafood. Some recent outbreaks are attributed to a rise in ocean temperatures, a trend that is likely to continue as a result of global warming and emphasizes the need to study the virulence mechanisms of the pathogen. V. parahaemolyticus utilizes a type III secretion system to inject effectors that disrupt signal transduction in eukaryotic hosts during infection. Herein, we describe an in vivo model of infection by V. parahaemolyticus using germfree mice. V. parahaemolyticus is recovered from the cecum and colon of mice infected by oral gavage. Mice infected with a pathogenic, wild type strain of V. parahaemolyticus exhibit intestinal inflammation characterized by epithelial damage, submucosal edema, crypt abscess and hyperplasia, and infiltration of the lamina propria by neutrophils. Using mutant strains of V. parahaemolyticus, we have determined that thermostable direct hemolysin, the most well characterized virulence factor produced by V. parahaemolyticus, and T3SS2, one of the two type III secretion systems present in this bacterium, both contribute to enteropathogenesis. Analysis of the expression of inflammatory cytokines IL-1? and IFN-gamma and chemokines KC, MIP-2 alpha, and CXCL-9 reveals that the duration of the inflammatory response is extended in the presence of TDH. In addition to delineating the roles of the virulence factors TDH, type III secretion system 1, and type III secretion system 2, in the infection process, we have developed an experimental system that will enable further characterization of type III effectors of V. parahaemolyticus.