Decontamination of Vibrio parahaemolyticus in fish by washing with hygienic seawater and impacts of the high level contamination in the gills and viscera.

The effect of washing in Vibrio parahaemolyticus contaminated and hygienic seawater on fish, and the frequency and level of natural V. parahaemolyticus contamination in fish were investigated. In the first experiment, live horse mackerel was experimentally kept in seawater artificially contaminated with V. parahaemolyticus. After washing in contaminated and hygienic seawater, the contamination in fish was quantitatively analyzed. Washing fish in the seawater contaminated with V. parahaemolyticus increases the contamination level on the surface and in the gills of the fish. Washing in hygienic seawater was effective in reducing the contamination in fish and cutting board surfaces, but not in the gills or viscera. In the second experiment, natural V. parahaemolyticus contamination in various fish caught by us was analyzed. V. parahaemolyticus was detected in 6 of 28 gill samples and 10 of 28 viscera samples of naturally contaminated fish. The means of V. parahaemolyticus level on gills were 3.3 and 3.9 log cfu/g, and those in viscera were 2.6 and 4.4 log cfu/g by culture method and a real-time PCR assay, respectively. These results indicate that the gills and viscera are able to spread the pathogens to fish meat as well as fish surface contamination by washing in the contaminated seawater. Washing with hygienic seawater and control of contamination from gills and viscera are critically important to prevent V. parahaemolyticus infections.

Comparative evaluation of the Desoxycholate Agar Nissui Food Stamp and swab methods for estimating coliform organisms in poultry processing plants after cleaning in Japan.

Bacterial control in poultry processing plants is very important, but the swab method for estimating bacterial contamination is somewhat troublesome in routine work. We compared the Desoxycholate Agar Nissui Food Stamp (DA-NFS) based on the agar contact method with the swab method to estimate coliform organisms from various equipments in four poultry processing plants after cleaning. Overall 104 surfaces for coliform organisms were evaluated. The results from 98 (94.2%) surfaces for coliform organisms were equivalent by the DA-NFS and swab methods and there were no significant differences between two methods (P > 0.05). The correlation coefficient between the DA-NFS and swab methods was 0.91. We conclude that the DA-NFS could be useful for routine coliform organisms examination in poultry processing plants after cleaning in Japan.

Growth kinetics of Vibrio parahaemolyticus O3:K6 under varying conditions of pH, NaCl concentration and temperature.

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 different 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 25 degrees C, 20 degrees C and 15 degrees C, pH 8, 7 and 5.8, and 1%, 3% and 7%, respectively. The bacteria grew most rapidly at 25 degrees C, 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.

Prevalence of pandemic thermostable direct hemolysin-producing Vibrio parahaemolyticus O3:K6 in seafood and the coastal environment in Japan.

Although thermostable direct hemolysin (TDH)-producing Vibrio parahaemolyticus has caused many infections in Asian countries, the United States, and other countries, it has been difficult to detect the same pathogen in seafoods and other environmental samples. In this study, we detected and enumerated tdh gene-positive V. parahaemolyticus in Japanese seafoods with a tdh-specific PCR method, a chromogenic agar medium, and a most-probable-number method. The tdh gene was detected in 33 of 329 seafood samples (10.0%). The number of tdh-positive V. parahaemolyticus ranged from <3 to 93/10 g. The incidence of tdh-positive V. parahaemolyticus tended to be high in samples contaminated with relatively high levels of total V. parahaemolyticus. TDH-producing strains of V. parahaemolyticus were isolated from 11 of 33 tdh-positive samples (short-necked clam, hen clam, and rock oyster). TDH-producing strains of V. parahaemolyticus were also isolated from the sediments of rivers near the coast in Japan. Representative strains of the seafood and sediment isolates were examined for the O:K serovar and by the PCR method specific to the pandemic clone and arbitrarily primed PCR and pulsed-field gel electrophoresis techniques. The results indicated that most O3:K6 tdh-positive strains belonged to the pandemic O3:K6 clone and suggested that serovariation took place in the Japanese environment.

[Survival of Vibrio parahaemolyticus serovar O3:K6 strains under acidic conditions].

The survival of Vibrio parahaemolyticus serovar O3:K6 strains and other serovars in the presence of acetic, citric and hydrochloric acids were studied. There were no differences in resistance to these acids between serovar O3:K6 and the other serovars. At pH 5.6, citric acid was more effective in reducing the number of viable cells of V. parahaemolyticus than acetic acid. However, at pH 4.5, acetic acid was more effective than citric acid. The number of viable cells decreased quickly in the presence of rice vinegar or wine vinegar at pH 4.0.