Colonization of shellfish by pathogenic Vibrios

Bacteria that are members of the Vibrio genus are ubiquitous in the marine environment and are part of the natural estuarine microflora. Several Vibrio species can accumulate in shellfish through filter feeding, and pose a significant threat to human health from important fishery resources. Little is known about the interactions of these microorganisms with shellfish that result in significant accumulation of the bacteria. Vibrio vulnificus can cause fatal septicemic infections in individuals who are immunocompromised or suffer from liver disease through consumption of raw shellfish harvested from warm water regions. In addition, the bacterium can cause severe necrotizing wound infections in otherwise healthy people who handle shellfish. Such infections impact the entire U.S. shellfish industry causing significant economic losses. Another vibrio, Vibrio parahaemolyticus, has a wider geographic distribution and is a significant source of shellfish-transmitted gastrointestinal illness in humans, with increased incidence during summer months. Our research is aimed at the characterization of surface structures called pili or fimbriae to ascertain their function in persistence of vibrios in oysters, as well as in human pathogenesis. Pili are thin (ca. 10 nm diameter) fiber-like structures that extend from bacterial cells and are often involved in cell to cell binding or attachment of a bacterium to a variety of biotic and abiotic surfaces. In initial studies on the role of a specific class of pili in V. vulnificus, designated type IV, we have demonstrated their role in adherence to human epithelial cells, biofilm formation, virulence in a mouse model, and persistence in oysters. We are currently examining the function of homologous pili in V. parahaemolyticus. If these factors prove to be responsible for the bacterium's ability to colonize oyster tissue, they may present a unique and specific target(s) for compounds designed to interfere with this attachment, leading to depuration methods that could potentially reduce or eliminate the organisms from oysters.