Vibrio parahaemolyticus, one of the most prevalent causes of acute gastroenteritis world-wide, is known to produce various virulence factors, among which thermostable direct haemolysin (Vp-TDH), the toxin responsible for the Kanagawa phenomenon, has been demonstrated to be the most important. Recently a haemolysin related to the Vp-TDH was recognized in Kanagawa phenomenon-negative clinical isolates of V. parahaemolyticus and was named Vp-TRH after Vp-TDH related haemolysin. Both Vp-TDH and Vp-TRH are composed of 165 amino acids and their amino acid sequence homology is about 67%. They have similar biological, immunological and physicochemical characteristics. Detailed structure and function relationship of Vp-TDH/TRH has been investigated. Evidence suggests that both Vp-TDH and Vp-TRH are important virulence factors in the pathogenesis of V. parahaemolyticus infections and that not only Vp-TDH-producing (i.e. Kanagawa phenomenon-positive) V. parahaemolyticus, but also Vp-TRH-producing ones are human pathogens.
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