Jun Takano

Detection of the thermostable direct hemolysin gene (tdh) and the thermostable direct hemolysin-related hemolysin gene (trh) of Vibrio parahaemolyticus by polymerase chain reaction

Polymerase chain reaction (PCR) protocols were established for specific detection of the tdh and trh genes, the virulence marker genes of Vibrio parahaemolyticus encoding two related hemolysins. The tdh and trh genes are known to have sequence divergence of up to 3.3% and 16%, respectively. Attempts were made to find suitable primer pairs and annealing temperatures to detect each gene without fail. DNAs extracted from 36 representative strains of V. parahaemolyticus were used in the initial screening with various combinations of primer pairs and annealing temperatures. The combinations of primer pairs and annealing temperatures selected were then tested with DNAs extracted from 227 more strains of V. parahaemolyticus and from 133 bacterial strains belonging to 40 species other than V. parahaemolyticus. PCR protocols (primer pairs and annealing temperatures) were established that gave identical results to those obtained with the tdh- and trh-specific polynucleotide probes. These protocols established for the tdh and trh genes could detect 400 fg (100 cells) of cellular DNA carrying the respective gene. Spike experiments demonstrated that the sensitivities of the established PCRs were reduced by a factor of 10(4)-10(5) by an inhibitor(s) present in a normal faecal sample, indicating the need for either DNA extraction or enrichment of the faecal sample in alkaline peptone water for 4 h before the PCR of faecal samples.

Non-isotopic microtitre plate-based assay for detecting products of polymerase chain reaction amplification: application to detection of the tdh gene of Vibrio parahaemolyticus

A non-isotopic microtitre plate-based assay method was devised for detection of products of the polymerase chain reaction. This assay involves affinity immobilization of the biotinylated amplification products in microtitre plate wells and their fluorescence detection by their hybridization with an oligonucleotide probe linked to alkaline phosphatase. An advantage of this procedure is that the immobilization and hybridization are carried out simultaneously in the wells, thus shortening the assay time. The assay method was applied to the detection of the tdh gene of Vibrio parahaemolyticus. Seven copies of the target chromosome could be detected in about 45 min after 35 cycles of amplification.