Improved Microbial Safety of Direct Ozone-Depurated Shellstock Eastern Oysters (Crassostrea virginica) by Superchilled Storage.

The effect of superchilled storage at -1°C on the microbial safety of oyster depurated with 0.2, 0.4, and 0.6 mg/L ozone was studied for 14 days. Fecal coliforms (4,100-16,000 MPN/100 g), Escherichia coli (1,500-3,650 MPN/100 g), Vibrio cholerae non-O1/non-O139 (13.0-102.0 MPN/g), and Salmonella spp. (2.270-3.035 × 103 CFU/g) were initially present in raw oysters. After 6 h depuration, fecal coliform counts decreased (P < 0.05) to 300, 20 and 20 MPN/100 g for 0.2, 0.4, and 0.6 mg/L treatments, while a 0.3 log decrease in control oysters was observed. Initial E. coli counts decreased (P < 0.05) in oysters to 50, 20, and 20 MPN/100 g for 0.2, 0.4, and 0.6 mg/L treatments, respectively. A 1 log reduction in V. cholerae non-O1/non-139 levels were observed in 0.4 and 0.6 mg/L-treatments after 2 and 4 h depuration. Salmonella spp. was not detected in oyster samples after 6 h depuration in 0.4 and 0.6 mg/L-ozone treatments. Considering the bacterial loads after depuration, at the end of superchilled storage the 0.4 mg/L-ozonated oysters attained lower (P < 0.05) fecal coliform levels (280 MPN/100 g) and E. coli counts in 0.4 and 0.6 mg/L-ozonated oysters (20 and 95 MPN/100 g, respectively). A 2-log decrease in V. cholerae non-O1/non-O139 levels on day 5 in 0.4 and 0.6 mg/L-ozonated oysters (< 0.3 MPN/g) was attained. V. cholerae non-O1/non-O139 counts in control oysters decreased 1 log on day 9 of superchilled storage. Salmonella spp. was not detected in ozonated and superchilled stored oysters. Levels of fecal coliforms, E. coli, Salmonella spp., and V. cholerae non-O1/non-O139 in non-ozone depurated oyster samples were higher than in control, 0.4 and 0.6 mg/L ozonated oyster samples during superchilled storage. The cumulative mortality rates after 14 days of storage for superchilled oysters (22.2%) was higher (P < 0.05) than 0.6 mg/L O3 (7.2%) and 0.4 mg/L O3 (5.8%) treatments, and control oysters (5.6%). pH values in control oysters decreased significantly (P < 0.05) throughout the storage period but not in oysters of both ozone treatments, indicating no detrimental effects on oyster survival. The results of this study suggest that superchilled storage enables ozonated shellstock oysters (0.4 mg/L-6 h) stored for 9 days to be safe human consumption.

[Growth and survival of total and pathogenic Vibrio parahaemolyticus in American oyster (Crassostrea virginica) under cold storage]. / Crecimiento y sobrevivencia de Vibrio parahaemolyticus en ostión americano (Crassostrea virginica) almacenado en refrigeración.

OBJECTIVE: To quantify Vibrio parahaemolyticus densities in American oyster (Crassostrea virginica) under cold storage. MATERIALS AND METHODS: 320 oysters were stored at 7°C for nine days and total and pathogenic densities were determined by the NMP-PCR methodology. RESULTS: V. parahaemolyticus tlh+ densities were observed on 0,3, and 6 days of storage at 1.134, 2.764 and 0.785 log10NMP/g, respectively, and pathogenic density trh+ on 0 and 3 days at 0.477 and 0.519 log10NMP/g, respectively; the pathogenic densities tdh+ (0.519 log10NMP/g), tdh+/trh+ (0.519 log10NMP/g), and tdh+orf8+ (-0.444 log10NMP/g) were detected on day 3 of storage. CONCLUSION: The results suggest that V. parahaemolyticus growth and pathogenic genes occurrence at 7°C involve changes in the genetic expression as a cold shock response, favoring V. parahaemolyticus survival and virulence, representing a health risk.

Crecimiento y sobrevivencia de Vibrio parahaemolyticus en ostión americano (Crassostrea virginica) almacenado en refrigeración / Growth and survival of total and pathogenic Vibrio parahaemolyticus in American oyster (Crassostrea virginica) under cold storage

Objetivo. Cuantificar las densidades de Vibrio parahaemolyticus en ostión americano (Crassostrea virginica) almacenado en refrigeración. Material y métodos. Se almacenaron 320 ostiones a 7 °C durante nueve días y se determinaron las densidades totales y patogénicas mediante la técnica NMP-PCR. Resultados. Se observaron densidades de V. parahaemolyticus tlh+ en los días 0,3 y 6 de almacenamiento con 1. 134,2.764 y 0.785 log10NMP/g, respectivamente, y en los días 0 y 3 la densidad patogénica trh+ con 0.477 y 0.519 log10NMP/g, respectivamente; las densidades patogénicas tdh+ (0.519 log10NMP/g), tdh+/trh+ (0.519 log10 NMP/g) y tdh+/orf8+ (-0.444 log10NMP/g) se detectaron al tercer día de almacenamiento. Conclusión. Los resultados sugieren que el crecimiento de V. parahaemolyticus y la ocurrencia de genes patogénicos a 7 °C involucran cambios en la expresión génica como una respuesta al estrés por frío. Esto contribuye a la sobrevivencia y virulencia de V. parahaemolyticus, lo cual representa un riesgo a la salud pública.

Objective. To quantify Vibrio parahaemolyticus densities in American oyster (Crassostrea virginica) under cold storage. Materials and methods. 320 oysters were stored at 7°C for nine days and total and pathogenic densities were determined by the NMP-PCR methodology. Results. V. parahaemolyticus tlh+ densities were observed on 0,3, and 6 days of storage at 1.134, 2.764 and 0.785 log10NMP/g, respectively, and pathogenic density trh+ on 0 and 3 days at 0.477 and 0.519 log10NMP/g, respectively; the pathogenic densities tdh+ (0.519 log10NMP/g), tdh+/trh+ (0.519 log10NMP/g), and tdh+orf8+ (-0.444 log10NMP/g) were detected on day 3 of storage. Conclusion.The results suggest that V. parahaemolyticus growth and pathogenic genes occurrence at 7°C involve changes in the genetic expression as a cold shock response, favoring V. parahaemolyticus survival and virulence, representing a health risk.

Environmental parameters influence on the dynamics of total and pathogenic Vibrio parahaemolyticus densities in Crassostrea virginica harvested from Mexico's Gulf coast.

The influence of environmental parameters on the total and pathogenic Vibrio parahaemolyticus seasonal densities in American oysters (Crassostrea virginica) was evaluated for 1 year. Harvesting site A yielded the highest mean densities of V. parahaemolyticus tlh+, tdh+/trh-, tdh-/trh+ and tdh+/trh+ during spring season at 2.57, 1.74, 0.36, and -0.40 log10 MPN/g, respectively, and tdh+/orf8+ during winter season (0.90 log10 MPN/g). V. parahaemolyticus tlh+ densities were associated to salinity (R(2)=0.372, P<0.022), tdh+/trh+ to turbidity (R(2)=0.597, P<0.035), and orf8+ to temperature, salinity, and pH (R(2)=0.964, P<0.001). The exposure to salinity and temperature conditions during winter and spring seasons regulated the dynamics of V. parahaemolyticus harboring potentially pathogenic genotypes within the oyster. The adaptive response of V. parahaemolyticus to seasonal environmental changes may lead to an increase in survival and virulence, threatening the seafood safety and increasing the risk of illness.

Seasonal abundance of total and pathogenic Vibrio parahaemolyticus isolated from American oysters harvested in the Mandinga Lagoon System, Veracruz, Mexico: implications for food safety.

The abundance of total and pathogenic Vibrio parahaemolyticus (Vp) strains in American oysters (Crassostrea virginica) harvested in two different harvest sites from the Mandinga lagoon System was evaluated monthly for 1 year (January through December 2012). Frequencies of species-specific genes and pathogenic genes exhibited a seasonal distribution. The annual occurrence of Vp with the species-specific tlh gene (tlh(+)) was significantly higher during the winter windy season (32.50%) and spring dry season (15.0%), with the highest densities observed during spring dry season at 283.50 most probable number (MPN)/g (lagoon bank A, near human settlements), indicating the highest risk of infection during warmer months. Pathogenic Vp tlh(+)/tdh(+) frequency was significantly higher during the winter windy and the spring dry seasons at 22.50 and 10.00%, respectively, with highest densities of 16.22 and 41.05 MPN/g (bank A), respectively. The tlh/trh and tdh/trh gene combinations were also found in Vp isolates during the spring dry season at 1.25 and 1.3%, respectively, with densities of 1.79 and 0.4 MPN/g (bank A), respectively. The orf8 genes were detected during the winter windy season (1.25%) with highest densities of 5.96 MPN/g (bank A) and 3.21 MPN/g (bank B, near mangrove islands and a heron nesting area). Densities of Vp tdh(+) were correlated (R(2) = 0.245, P < 0.015) with those of Vp orf8(+). The seasonal dynamics of Vp harboring pathogenic genes varied with seasonal changes, with very high proportions of Vp tdh(+) and Vp orf8(+) isolates in the winter windy season at 46.2 and 17.0%, respectively, which suggests that environmental factors may differentially affect the abundance of pathogenic subpopulations. Although all densities of total Vp (Vp tlh(+)) were lower than 10(4) MPN/g, thus complying with Mexican regulations, the presence of pathogenic strains is a public health concern. Our results suggest that total Vp densities may not be appropriate for assessing oyster contamination and predicting the risk of infection. Evaluation of the presence of pathogenic strains would be a better approach to protecting public health.