The leading cause of food poisoning in both Taiwan and Japan is Vibrio parahaemolyticus infection, whose mechanism of enteropathogenesis is still unclear. To evaluate whether surface components are responsible for the intestinal adhesion of V. parahaemolyticus, we have developed a novel method for isolating the capsular polysaccharide (CPS) from V. parahaemolyticus (serotype O4:K8). We found that culturing of V. parahaemolyticus in broth for 1 week or more changed the colony form of the bacteria on an agar plate from opaque to translucent. The translucent colonies of V. parahaemolyticus contained little CPS and exhibited a much lower level of adherence to epithelial cells (Int-407) than the opaque colonies of the bacteria. Incubation of V. parahaemolyticus in medium supplemented with bile increased the levels of CPS and adherence. Treatment of V. parahaemolyticus with anti-CPS but not anti-LPS serum decreased the level of bacterial adherence. In addition, purified CPS bound to epithelial cells in a dose-dependent manner. Intranasal administration of CPS to mice in the presence of adjuvants such as immunostimulatory sequence oligodeoxynucleotides or cholera toxin elicited CPS-specific mucosal and systemic immune responses. These results indicate that CPS plays an important role in the adherence of V. parahaemolyticus to its target cells and may be considered a potential target for the development of a vaccine against this pathogen.Vibrio parahaemolyticus, a widely distributed gram-negative facultative anaerobic bacillus that causes acute gastroenteritis, was first isolated from its victims in 1950 by Fujino et al. (14). Under favorable conditions, the doubling time of V. parahaemolyticus can be as short as 9 min (26), enabling the organism to multiply rapidly. The onset of the illness usually takes place 3 to 24 h after consumption of V. parahaemolyticus-contaminated food. The symptoms include diarrhea, abdominal cramps, nausea, vomiting, headache, and low-grade fever (19). Exotoxins of the organism, such as thermostable direct hemolysin and its related toxin, have been intensively studied. It is generally believed that these exotoxins alone are not sufficient to generate the pathogenicity of the organism (19,36).Before enteric pathogens can cause disease, they usually adhere to, replicate in, and produce virulence factors on or in epithelial cells of the enteric tract. The adherence of V. parahaemolyticus to epithelial cell lines has been evaluated in several in vitro studies (6,7,16,43 (8,22,41). Recently, culturing of V. parahaemolyticus with bile or deoxycholate was shown to increase not only the bacterial capsule size but also the production of a uronic acid-containing capsule and to enhance the level of adherence to epithelial cells (32). For other enteric bacteria, it has been shown that capsule size can play a major role in virulence (8,45) and that the production of a uronic acid-containing extracellular capsule enables the bacteria to aggregate and adhere to intestinal cells (32). Therefore, it is possi...

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