The Vibrio genus consists of several species. V cholerae, V vulnificus, and V parahaemolyticus are significant with respect to foods and human health. 13 Vibrios are naturally present in marine environments. V parahaemolyticus is usually associated with coastal and estuary waters and can be found in fish, shellfish, and crustaceans harvested from these waters. Environmental isolation of V parahaemolyticus is dependent upon water temperature: when the temperature falls below 15°C, it cannot be isolated from water; however, survival during winter is thought to be due to survival in sediments. 14
With respect to cellular morphology, V parahaemolyticus cells are facultative Gram-negative short to comma-shaped rods possessing motility by a single polar flagellum. They are metabolically both oxidative and fermentative and most importantly obligate halophiles (salt loving), which is used to separate V parahaemolyticus from V cholerae. 13
V parahaemolyticus is the leading cause of foodborne illness in Japan and has caused outbreaks in the United States. The most common syndrome is watery diarrhea that affects patients 4 to 96 h after consumption and lasts about 3 days. However, a high ingestion of greater than 105 cells can produce dysentery syndrome. Symptoms include mucus and blood in stools, affecting patients just 20 min to 9 h after ingestion and lasting about 2.5 days. This syndrome usually occurs in summer to early fall. The mechanism of pathogenecity is not well known, but most clinical isolates exhibit a thermostable hemolysin toxin responsible for the Kanagawa phenomenon. 13
The enrichment, isolation, and identification of members of the genera Vibrio are based upon their ability to grow well at alkaline pH. V parahaemolyticus is further characterized based upon its requirement for NaCI for growth.