Contribution of the tdh1 gene of Kanagawa phenomenon-positive Vibrio parahaemolyticus to production of extracellular thermostable direct hemolysin.

Kanagawa phenomenon-positive strains of Vibrio parahaemolyticus contain two copies of the tdh gene (tdh 1 and tdh 2) encoding thermostable direct hemolysin (TDH). Previous studies suggested that the tdh 2 gene, but not the tdh 1 gene, was responsible for production of extracellular TDH. In this study, a tdh 2-deficient isogenic mutant of Kanagawa phenomenon-positive strain AQ3815 was constructed by a suicide vector-mediated in vivo recombination method. The intact tdh 1 gene in the mutant contributed little to Kanagawa phenomenon on Wagatsuma agar but produced TDH in broth media, accounting for 0.5-9.4% of total extracellular TDH of AQ3815.