Vibrio parahaemolyticus infection: understanding the host-pathogen interactions

Abstract

Vibrio parahaemolyticus, a Gram-negative bacterium, is the leading cause of seafood-related bacterial gastroenteritis in the United States. Most commonly associated with the ingestion of raw oysters, this emerging pathogen can causes self-limiting gastrointestinal infection, wound infection and, in the immunocompromised host, significant systemic disease leading to death. Though the frequency of raw oyster consumption is unknown, approximately 20% of the United States population (60 million) are at increased risk of infection due to immunocompromised conditions [1]. In addition, the CDC has recently reported a 39% increase in the number of culture confirmed Vibrio infections since 2006-2008 [2]. There is a dearth of literature regarding the host response to infection, the genes required for organism survival within the host, and pathogen elimination. Therefore, in order to elucidate the immune response to infection, we developed an in vitro model using the virulent clinical isolate V. parahaemolyticus RIMD 2210633, an O3:K6 serotype. Additionally, we investigated the host response to several genes hypothesized to be required for organism virulence. First, we determined that this isolate infects murine macrophage stimulating the production of proinflammatory cytokines and increasing surface protein expression of the activation markers CD86, CD14, MHC II, and CD40 on RAW 264.7 macrophage. Also, we investigated the macrophage cell death response induced by V. parahaemolyticus infection and determined it was mediated by an undefined mechanism independent of the NLRP3 inflammasome, caspase-1, cathepsin B, and IL-1β. Next, we confirmed infection stimulates bone marrow-derived macrophage (BMDMs) to produce reactive oxygen species (ROS). And in response to ROS production by macrophage, V. parahaemolyticus was found to induce bacterial antioxidant genes encoding anti-oxidant enzymes, such as AhpCF, catalases, and glutaredoxin to facilitate pathogen survival. In conclusion, we have characterized aspects of macrophage activation in response to infection with V. parahaemolyticus, as well as adaptations acquired by this gastrointestinal pathogen to evade host innate responses that may potentially contribute to pathogenesis by preventing rapid elimination from infected host tissues.