A Fluorogenic Assay for the Rapid Detection of Some Vibrio Species Inciuding Vibrio parahaemolyticus in Foods

A rapid assay method for some Vibrio species including Vibrio parahaemolyticus was developed. The assay involved the enrichment culture of Vibrio species in BSP-HP medium (0.2% bacto-tryptone, 2% sodium chloride, 250 units/ml polymyxin B sulfate, 0.025% sodium hexametaphosphate, pH 8.5) and the specific measurement of intracellular trypsin-like activity by using the fluorogenic substrate benzoyl-L-arginine-7-aminomethylcoumarin. In BSF-HP medium, growth and trypsin-like activity of bacteria other than V. parahaemolyticus, V. alginolyticus and V. harveyi were suppressed. Although trypsin-like enzyme in food samples interfered with the fluorogenic assay, the interference could be overcome by the addition of 1 mM EDTA to the reaction mixture. Using this fluorogenic assay with commercial seafoods, 400 cells of V. parahaemolyticus per gram of food sample were detected within 8 hr. Trypsinlike activity measured by the assay was proportional to the number of V. parahaemolyticus determined by the conventional BTB teepol agar plating method (correlation coefficient r= 0.97). In the medium, V. alginolyticus, one of the V. parahaemolyticus-allied bacteria, and V. harveyi also showed vigorous growth and high trypsin-like activity. A more specific culture condition for V parahaemolyticus is required, and further investigation is in progress.