Investigating Vibrio parahaemolyticus interactions with the Pacific oyster, Crassostrea gigas

Graduation date: 2013Vibrio parahaemolyticus is a Gram-negative, halophilic, human pathogenic bacterium ubiquitous in the marine environment. Like many Vibrio species, V. parahaemolyticus commonly associates with shellfish, particularly oysters. Ingestion of a raw or under cooked oysters contaminated with V. parahaemolyticus can cause gastroenteritis, which is typically self-limiting and rarely causes death. Globally, oyster production is highly lucrative, especially on the West Coast of the United States where approximately 60% of oyster production occurs each year. Outbreaks of V. parahaemolyticus can result in a significant public health problem as well as an economic burden for the oyster farms implicated in the outbreak. With the increase in overall V. parahaemolyticus outbreaks, improved post-harvest processing strategies have been developed to reduce this natural contaminant. Depuration was developed to allow shellfish to purge contaminants from their tissues into the clean, flowing seawater where they are held. This post-harvest processing technique can typically reduce fecal contaminants from the oyster tissues but is relatively ineffective at eliminating V. parahaemolyticus and other Vibrio species.. Thus, improved methods for reducing this and other human pathogenic Vibrio are needed to effectively produce safer oysters for the consumer. To develop more effective and novel V. parahaemolyticus intervention strategies, first we must identify the factors that are involved in V. parahaemolyticus colonization of the oyster, allowing them toresist depuration. This study sought to investigate specific factors utilized by V. parahaemolyticus and, in the process, determined that various strains of V. parahaemolyticus have different alleles of the Type IV pili, mannose-sensitive hemagglutinin (MSHA)and chitin-regulated pilus (PilA). In addition, we expanded our investigations into the allelic diversity of MSHA and PilA from Vibrio cholerae and Vibrio vulnificus and found that V. cholerae strains that possess the Type IV toxin co-regulated pilus (TCP) maintained highly conserved MSHA and PilA sequences while strains of V. cholerae without TCP, and all of the V. vulnificus and V. parahaemolyticus strains examined, had highly divergent sequences with no discernable connection to isolation source or observed phenotype. Following that discovery, we determined that Type I, and Type IV pili, as well as polar and lateral flagellar systems contribute to V. parahaemolyticus persistence in the Pacific oyster during depuration, while Type III secretion systems and phase variation do not. Overall, we have identified factors involved in colonization of the Pacific oyster by V. parahaemolyticus. Future studies investigating conditions that affect pili and flagella production in V. parahaemolyticus may provide novel depuration conditions that could easily and effectively increase the efficiency of oyster depuration, ultimately reducing the risk of seafood-borne illness by V. parahaemolyticus associated with oysters