VIBRIOSIS (Vibrio parahaemolyticus ibrio parahaemolyticus)Although most other known food-poisoning syndromes may be contracted from a variety of foods, V. parahaemolyticus gastroenteritis is contracted almost solely from seafood. When other foods are involved, they represent cross-contamination from seafood products. Another unique feature of this syndrome is the natural habitat of the etiological agent-the sea. In addition to its role in gastroenteritis, V. parahaemolyticus is known to cause extraintestinal infections in humans.The genus Vibrio consists of at least 28 species, and 3 that are often associated with V. parahaemolyticus in aquatic environments and seafood are V. vulnificus, V. alginolyticus, and V. cholerae. Some of the distinguishing features of these species are noted in Table 28-1, and the syndromes caused by each are described below.V. parahaemolyticus is common in oceanic and coastal waters. Its detection is related to water temperatures, with numbers of organisms being undetectable until the water temperature rises to around 19-20 • C. A study of the Rhode River area of the Chesapeake Bay showed that the organisms survive in sediment during the winter and later are released into the water column, where they associate with the zooplankton from April to early June. 62 In ocean waters, they tend to be associated more with shellfish than with other forms. 79 They have been demonstrated to adsorb onto chitin particles and copepods, whereas organisms such as Escherichia coli and Pseudomonas fluorescens do not. 62 This species is generally not found in the open oceans, and it cannot tolerate the hydrostatic pressures of ocean depths. 111
Growth ConditionsV. parahaemolyticus can grow in the presence of 1-8% NaCl, with best growth occurring in the 2-4% range. 110 It dies off in distilled water. It does not grow at 4 • C, but growth between 5 • C and 9 • C has been demonstrated at a pH 7.2-7.3 and 3% NaCl, or at a pH of 7.6 and 7% NaCl (Table 28-2).