Contribution of the tdh 1 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 (tdh1 and tdh2) encoding thermostable direct hemolysin (TDH). Previous studies suggested that the tdh2 gene, but not the tdh1 gene, was responsible for production of extracellular TDH. In this study, a tdh2-deficient isogenic mutant of Kanagawa phenomenon-positive strain AQ3815 was constructed by a suicide vector-mediated in vivo recombination method. The intact tdh1 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.