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The occurrence of the hemolysin genes, tdh and trh, in Vibrio parahaemolyticus strains isolated from environmental samples collected in two French coastal areas, clinical samples, and seafood products imported into France was studied. Polymerase chain reaction (PCR) with two sets of primers was used to detect the hemolysin genes. Most of the clinical isolates (91%) and 1.5% of the isolates from seafood possessed the hemolysin genes. Three and fifteen percent, respectively, of the two groups of environmental strains carried the hemolysin genes depending on the geographic site. The tdh and trh genes play important roles in virulence. Thus, our results indicate that pathogenic V. parahaemolyticus isolates are present in French coastal areas and in seafood imported into France. Furthermore, they may also be present in French seafood products.

We compared the efficiencies of biochemical methods and polymerase chain reaction (PCR) for the identification of Vibrio parahaemolyticus strains. The 122 isolates studied, identified by biochemical tests as V. parahaemolyticus or Vibrio alginolyticus, were tested by R72H PCR assay. The results obtained with the two methods were consistent for 90% of the strains studied. PCR amplification of the R72H fragment generated two unique amplicons, 387 bp and 320 bp in length. For 11% of the strains from seawater, the results of biochemical identification did not correlate with PCR results. DNA-DNA hybridization experiments provided evidence that some strains identified as V. alginolyticus in biochemical tests should be considered members of the V. parahaemolyticus species. We therefore suggest that biochemical tests are not accurate enough for the identification of V. parahaemolyticus isolates and we demonstrate that amplification of the R72H fragment, whether the amplicon is 320 bp or 387 bp long, is a powerful tool for the reliable identification of V. parahaemolyticus.