Performance of Cold Chains for Chesapeake Bay Farmed Oysters and Modeled Growth of Vibrio parahaemolyticus

ABSTRACT Temperature-controlled supply chains (cold chains) require an unbroken chain of refrigeration to maintain product quality and safety. This study investigated cold chains for farmed oysters raised in the Chesapeake Bay, one of the largest shellfish-growing regions in the United States, and sold live to the half-shell market in surrounding states. Temperature sensors were used in boxes of oysters from February to September 2017, which generated 5,250 h of temperature data. Thirty-nine businesses participated in the temperature sensor study, and 26 of those businesses participated in interviews to further understand how cold chains function. Internal oyster temperatures were measured above 50°F (10°C) for over 1 h in 19% (7 of 36) of shipments, which is a temperature that exceeds National Shellfish Sanitation Program criteria. The highest internal oyster temperature recorded in any shipment was 54.5°F (12.5°C). Some parts of the cold chain had difficulty maintaining storage temperatures below 45°F (7.2°C) in warmer months when Vibrio control plans were in effect. We modeled the effects of temperature on Vibrio parahaemolyticus. The model predicted moderate bacterial growth before oysters were under temperature control, but cold chains prevented further bacterial growth and provided a moderate drop-off in V. parahaemolyticus abundance.

Mermaid: A Shellfish Sanitation Model Providing Additional Metrics for the Classification of Shellfish Growing Areas of Virginia (USA), Managed by the Direct Rule Method

The Virginia Department of Shellfish Sanitation (VDSS) manages shellfish growing areas using the Direct Rule method, by directly comparing the Geometric Mean and Estimated 90th Percentile of fecal coliform concentrations to the U.S. National Shellfish Sanitation Program (NSSP) standard. The agency closes the area to harvest if fecal coliform concentrations exceed the NSSP limit and the area is not reopened until concentrations fall below the NSSP limit. The VDSS originally used the NSSP 3-Tube test (14/49 Standard), and transitioned to the NSSP Membrane Filtration Test (MFT, 14/31 Standard) in August 2007. In this article we focus on a VDSS 13-plus year dataset of fecal coliform concentrations from 127,320 water samples collected from 2,193 sampling stations in 103 shellfish growing areas located in Virginia’s state waters. Our goal is to introduce a new shellfish sanitation model, Mermaid, which provides additional metrics to the NSSP statistical procedures for managing shellfish growing areas under the Direct Rule method, using calculated datasets, with uniform and mixed samples. We also examine if the additional metrics, which are based on the upper limits of Estimated 90th Percentile values of fecal coliform concentrations, increase the health safety of harvested shellfish managed under the Direct Rule method. Keywords: Aquaculture, Computer software, Decision support system, Diagnosis, Fecal coliform, Sanitation model, Shellfish harvesting

Watershed-Based Planning for Murrells Inlet: Source Assessment of Fecal Bacteria Using Volunteer and Shellfish Sanitation Program Data

A watershed-based plan was recently developed for Murrells Inlet, a moderately tidal, euhaline estuary located on the northern coast of South Carolina. One of the goals of this planning effort was to collate and analyze existing data to refine assessments of the sources of fecal coliform detected by SC DHEC’s shellfish monitoring program. Coastal Carolina University’s Waccamaw Watershed Academy (WWA) was engaged to lead this data analysis effort. The most important sources identified were urbanized wildlife and canines. Results from the data analyses were used to prioritize subwatersheds for remediation. This has led to proposed strategies that focus on interception and treatment of stormwater runoff as well as volume reduction, dredging of tidal creek sediments, and outreach education for pet waste control.

Effect of Cooling Rates and Temperatures on Quality and Safety of Quahog Clams (Mercenaria mercenaria)

The model ordinance in the National Shellfish Sanitation Program's Guide for the Control of Molluscan Shellfish was initially established for oysters; however, the clam industry also follows the protocol. Rapid cooling during periods when the growing waters exceed 80°F (26.7°C) results in cold shock, which causes unacceptable mortalities in clams. The clam industry was looking for a procedure to lower the clams to the standard temperature while minimizing shell shock mortalities during the warm summer months. Three tempering treatments were examined, and total aerobic plate counts (APCs) and most-probable-number (MPN) counts of Vibrio, V. parahaemolyticus, and fecal coliforms were enumerated. In treatment 1 (control), clams were harvested, held for 5 h at 90°F (32.2°C), and then moved to 45°F (7.2°C) for storage. In treatment 2, clams were harvested and held for 5 h at 90°F (32.2°C), followed by 12 h at 65°F (18.3°C) and 12 h at 55°F (12.8°C), and then were moved to 45°F (7.2°C) for long-term storage. In treatment 3, clams were harvested and held for 5 h at 90°F (32.2°C), followed by 24 h at 55°F (12.8°C) before being moved to 45°F (7.2°C) for long-term storage. Three replicate trials were performed with triplicate analyses during late June through early to mid-August. The current National Shellfish Sanitation Program standard is treatment 1; it contained statistically (P ≤ 0.05) higher total APCs than treatments 2 and 3 throughout the 21-day storage period. APCs ranged from 2.3 ×104 immediately after harvest to 2.7 ×106, 1.6 ×105, and 4.8 ×105 for treatments 1, 2, and 3, respectively, after 14 days of storage. A statistical analysis showed that treatments 2 and 3 had significantly lower total MPN per gram Vibrio than treatment 1 on day 7 but were equal to treatment 1 on days 1 and 14. MPN per gram for V. parahaemolyticus was statistically lower in treatments 2 and 3 than in treatment 1 on storage days 1 and 7. However, on day 14, treatment 3 was significantly lower than treatments 1 and 2. There was no statistical difference for fecal coliforms. The greatest mortality occurred in treatment 1 (87.4%), followed by treatment 2 (83.3%) and treatment 3 (66.0%). The outcome of this research clearly shows that treatments 2 and 3 can cool clams to a temperature of 45°F (7.2°C) without compromising quality or safety and can reduce the number of dead clams introduced into the marketplace.

Effects of Flash Freezing, Followed by Frozen Storage, on Reducing Vibrio parahaemolyticus in Pacific Raw Oysters (Crassostrea gigas)

This study investigated the effects of flash freezing, followed by frozen storage, on reducing Vibrio parahaemolyticus in Pacific raw oysters. Raw Pacific oysters were inoculated with a five-strain cocktail of V. parahaemolyticus at a total level of approximately 3.5 × 105 most probable number (MPN) per gram. Inoculated oysters were subjected to an ultralow flash-freezing process (−95.5°C for 12 min) and stored at −10, −20, and −30°C for 6 months. Populations of V. parahaemolyticus in the oysters declined slightly by 0.22 log MPN/g after the freezing process. Subsequent storage of frozen oysters at −10, −20, and −30°C resulted in considerable reductions of V. parahaemolyticus in the oysters. Storing oysters at −10°C was more effective in inactivating V. parahaemolyticus than was storage at −20 or −30°C. Populations of V. parahaemolyticus in the oysters declined by 2.45, 1.71, and 1.45 log MPN/g after 1 month of storage at −10, −20, and −30°C, respectively, and continued to decline during the storage. The levels of V. parahaemolyticus in oysters were reduced by 4.55, 4.13, and 2.53 log MPN/g after 6 months of storage at −10, −20, and −30°C, respectively. Three process validations, each separated by 1 week and conducted according to the National Shellfish Sanitation Program's postharvest processing validation–verification interim guidance for Vibrio vulnificus and Vibrio parahaemolyticus, confirmed that a process of flash freezing, followed by storage at −21 ± 2°C for 5 months, was capable of achieving greater than 3.52-log (MPN/g) reductions of V. parahaemolyticus in half-shell Pacific oysters.

Effectiveness of Icing as a Postharvest Treatment for Control of Vibrio vulnificus and Vibrio parahaemolyticus in the Eastern Oyster (Crassostrea virginica)

The focus of this research was to investigate the efficacy of icing as a postharvest treatment for reduction of the levels of Vibrio vulnificus and Vibrio parahaemolyticus in commercial quantities of shellstock oysters. The experiments were conducted in June and August of 2006 and consisted of the following treatments: (i) on-board icing immediately after harvest; (ii) dockside icing approximately 1 to 2 h prior to shipment; and (iii) no icing (control). Changes in the levels of pathogenic Vibrio spp. during wholesale and retail handling for 2 weeks postharvest were also monitored. On-board icing achieved temperature reductions in all sacks in accordance with the National Shellfish Sanitation Program standard, but dockside icing did not meet this standard. Based on one-way analysis of variance, the only statistically significant relationship between Vibrio levels and treatment occurred for samples harvested in August; in this case, the levels of V. vulnificus in the noniced oysters were significantly higher (P < 0.05) than were the levels in the samples iced on-board. When analyzing counts over the 14-day storage period, using factorial analysis, there were statistically significant differences in V. vulnificus and V. parahaemolyticus levels by sample date and/or treatment (P < 0.05), but these relationships were not consistent. Treated (iced) oysters had significantly higher gaping (approximately 20%) after 1 week in cold storage than did noniced oysters (approximately 10%) and gaping increased significantly by day 14 of commercial storage. On-board and dockside icing did not predictably reduce the levels of V. vulnificus or V. parahaemolyticus in oysters, and icing negatively impacted oyster survival during subsequent cold storage.

Étude de la contamination microbienne des myes (Mya arenaria) de la rive nord de l'estuaire maritime du fleuve Saint-Laurent (Québec, Canada)

The aims of the present study were to assess the microbial quality of Mya arenaria clams from the north shore of the St. Lawrence River estuary and to validate various microbial indicator microorganisms of bivalve mollusks contamination. Clams were collected from nine sites, including four harvesting sites closed by virtue of the Canadian Shellfish Sanitation Program (CSSP). Six contamination indicators (fecal coliforms, somatic coliphages, F-specific coliphages, fecal streptococci, Clostridium perfringens, and Escherichia coli) and four pathogens (Campylobacter sp., Cryptosporidium parvum, Giardia sp., and Salmonella sp.) were identified in the clams. Indicators sensibility, specificity and predictive values with respect to the presence of pathogens were calculated. Pathogenic microorganisms detection frequency in clams was important (92%). Globally, pathogens tend to be less frequently detected in opened harvesting sites (p = 0.086). Although the assessed indicators were not perfect, when F-specific coliphages are associated with E. coli or fecal coliforms, a good sensibility (62%–64%) and good positive predictive value (88%) with respect to the investigated pathogens are obtained.Key words: mollusks, coliforms, Giardia, Cryptosporidium, Campylobacter.[Journal translation]

Effects of a Commercial Heat-Shock Process on Vibrio vulnificus in the American Oyster, Crassostrea virginica, Harvested from the Gulf Coast

Oysters (Crassostrea virginica) harvested from the Gulf Coast, containing 102 to 104 most probable number (MPN) per gram of Vibrio vulnificus, were subjected to a commercial heat-shock process. After 1 to 4 min at internal oyster meat temperatures exceeding 50°C, shellstock oysters were shucked, chilled, washed, and packed. V. vulnificus and total bacterial levels in Gulf Coast oysters were significantly reduced from 1 to 4 logs in the finished product. Similar reductions were not observed in shellstock oysters that were subject to conventional processing. Under the National Shellfish Sanitation Program, heat shocking is an acceptable process to use to assist in the shucking of shellstock. This research revealed that the heat-shock process may also serve to significantly reduce V. vulnificus in summer Gulf Coast oysters.