It was attempted to detect thermostable direct hemolysin (TDH) producing Vibrio parahaemolyticus in food by polymerase chain reaction (PCR) with VPD-1 and-2 primers (Shimadzu). This primer pair could amplify a 251-bp resion in tdh gene which encoded sequence to produce TDH.
The KAP-RPLA “Seiken” (Denka Seiken) test showed that 35 (92%) of 38 strains from patients infected with V. parahaemolyticus produced TDH and 7 (100%) from food didn't. When these 45 strains were subjected to PCR, 251-bp products were demonstrated exclusively in TDH-positive strains. PCR deteced the strain producing TDH in minced prawn mixed experimentally with 103 cfu/g or more bacteria. PCR detected even fewer bacteria in prawn, if the supernatant of the enrichment culture incubation was tested. When a TDH-positive strain and more than hundred-fold negative one were inoculated together to prawn, it was recognized that the growth of positive one was inhibited by negative one during incubation. Then, PCR failed to detect the TDH-positive strain in prawn.
It was indicated, however that this PCR was successfully applied to detect TDH producing V. parahaemolyticus in food incriminated for food poisoning due to these bacteria, because such food must contain a large number of pathogenic bacteria.
