CONSTRUCTION AND CHARACTERIZATION OF AN ISOGENIC MUTANT OF VIBRIO-PARAHAEMOLYTICUS HAVING A DELETION IN THE THERMOSTABLE DIRECT HEMOLYSIN-RELATED HEMOLYSIN GENE (TRH)

A mutant, Vp-MX02 having a deletion in the gene (trh) for the thermostable direct hemolysin-related hemolysin (TRH) was constructed by double-crossover gene conversion from a TRH-producing Vibrio parahaemolyticus strain, TH3996. The deleted region was the upstream half of trh. Hemolysis was completely lost, and TRH antigen was undetectable in the mutant. Administration of the mutant into ligated rabbit small intestines elicited partial, but apparent, fluid accumulation. These results suggest that the enterotoxicity of TRH-producing V. parahaemolyticus TH3996 may be attributed to the remaining C-terminal of TRH or, more likely, to an unknown virulence factor(s) in addition to TRH.