We have developed a new, effective procedure for detecting Vibrio parahaemolyticus in seafoods using enrichment and plating onto a chromogenic agar medium. Samples were cultured in salt Trypticase soy broth, which is a nonselective medium, and then a portion of the culture was cultured with salt polymyxin broth, which is a selective medium for V. parahaemolyticus. This two-step enrichment was more effective than the one-step enrichment in salt polymyxin broth alone. The enrichment cultures were then plated onto a new chromogenic agar containing substrates for beta-galactosidase. The V. parahaemolyticus colonies developed a purple color on this growth medium that distinguished them from other related bacterial strains. V. parahaemolyticus was isolated more frequently from naturally contaminated seafood samples using the chromogenic agar than thiosulfate citrate bile salts sucrose agar medium, which is currently used for the isolation of V. parahaemolyticus. Our findings suggest that this new enrichment and isolation scheme is more sensitive and accurate for identifying V. parahaemolyticus in seafood samples than previously used methods.Vibrio parahaemolyticus is a major food-borne pathogen that causes worldwide health problems. Prevention of V. parahaemolyticus contamination of foods, especially contamination with serotype O3:K6, which has been associated with recent outbreaks (3,5,6,7), is an important public health concern. It has been observed that the new O3:K6 clone of V. parahaemolyticus spread to Taiwan, Laos, Japan, Thailand, Korea, and the United States between 1997 and 1998 (10).To establish effective control measures to reduce the risk of V. parahaemolyticus infection and to ensure the safety of foods, efficient analytical methods for the detection of V. parahaemolyticus in foods and the environment must be available. Selective enrichment with alkaline peptone water (APW) or salt polymyxin broth (SPB) and plating of the enrichment culture onto thiosulfate citrate bile salts sucrose (TCBS) agar have been widely used for selective isolation of V. parahaemolyticus from foods. Although this existing method for detecting this organism in foods is inadequate, V. parahaemolyticus isolation schemes have not been carefully studied. It has been observed for other bacteria that nonselective enrichment prior to selective enrichment is effective for the detection of bacteria injured by various environmental stresses (4, 13). Therefore, we studied the effectiveness of nonselective enrichment prior to selective enrichment for V. parahaemolyticus. Furthermore, we have noted in a survey of seafoods that V. parahaemolyticus colonies on TCBS agar are difficult to distinguish visually from other bacterial colonies, since they can be covered by a yellow color produced by sucrose-fermenting bacteria. To develop a more efficient method, we studied the effectiveness of a method involving a two-step enrichment with nonselective and selective media and plating onto a chromogenic agar medium. This agar medium containing substrat...

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The growth responses of Vibrio parahamolyticus to pH, NaCl concentration and temperature changes were studied using serotype O3 : K6 and other strains. Growth curves were obtained for 27 di#erent sets of conditions, comprised of three levels of NaCl concentration, pH and temperature. The temperature, pH and NaCl concentrations most favorable for growth were in the order of 25ῌ, 20ῌ and 15ῌ, pH 8, 7 and 5.8, and 1῍, 3῍ and 7῍, respectively. The bacteria grew most rapidly at 25ῌ, at a pH of 7 or 8 in the presence of 1῍ or 3῍ NaCl, with the population (initial, ca. 2.5 log CFU/mL) reaching a level log 7 CFU/mL at 12 h. A growth predictive model using the Gompertz equation was generated from the experimental data for any combination of NaCl concentration, pH and temperature within the range used in this study.

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