Thermostable Direct Hemolysin (TDH) in Foods and the Effect of a Few Digestive Enzymes on TDH Production by Vibrio parahaemolyticus

Abstract

Thermostable direct hemolysin (TDH) produced by Vibrio parahaemolyticus has been supposed to be the greatest causative factor for the enteropathogenicity. However, there have been no reports concerning the existence of TDH in any foods. We tried to detect it in some foods which are well known as the causative foodstuffs of this foodborn disease, using the method of the human red blood cell lysis system. Fresh shrimp showed the lytic activity only when the strain was inoculated. Shirasu-boshi (salted, small and half-dried sardines) already showed the lytic activity without the strain, and increased activity was observed after the inoculation. The lytic activity of fresh oyster was not changed significantly after the inoculation. The pre-incubation with trypsin or pancreatin for 1 hr at 37°C increased the lytic activity in fresh shrimp.
These findings auggest that TDH is produced not only in some foods, but also in our small intestine by V. parahaemolyticus.