A joint study by local oyster growers and researchers at the Virginia Institute of Marine Science shows that moving farmed oysters into saltier waters just prior to harvest nearly eliminates the presence of a bacterium that can sicken humans.
The findings—reported by VIMS professors Kim Reece and Howard Kator, and local oyster growers Thomas Gallivan, A.J. Erskine, and Tommy Leggett—may offer a relatively low-cost solution to a controversial change in FDA regulations that many growers believe will eventually affect the oyster industry in Chesapeake Bay.
The Food and Drug Administration's regulatory change, set to take affect during this year's harvest season in the Gulf of Mexico, requires Gulf shellfish growers to eliminate the bacterium Vibrio vulnificus from shellfish through the use "post-harvest processing" or "PHP." PHP methods include low-temperature pasteurization, flash freezing, high pressure, and low-dose irradiation.
The FDA rule does not currently pertain to oyster growers in Chesapeake Bay, but local growers and scientists believe it will eventually apply here and in other U.S. oyster-growing regions as well.The FDA says PHP is needed to eliminate Vibrio vulnificus from Gulf shellfish because the bacterium is implicated in about 25 deaths and 90 cases of illness in the U.S. each year. Most of these illnesses result from consumption of raw oysters and clams from the Gulf by persons with liver disorders (including hepatitis, cirrhosis, and liver cancer); hemochromatosis (a disorder in which too much iron is absorbed from the gastrointestinal tract); or diabetes; and those with weakened immune systems due to treatments for HIV/AIDS or cancer.
Some members of the Virginia and Gulf aquaculture industries counter that existing PHP methods are too costly for an industry dominated by small, local operators; change the texture and taste that oyster lovers crave; and would duplicate existing oyster-sanitation rules. They also note that infections from Vibrio vulnificus account for only 0.3% of deaths attributed to food-borne illnesses, and argue that the FDA should focus on reducing deaths from Salmonella and Listeria instead.
An Alternative Approach
The VIMS-industry team contends that moving oysters to saltier water—what they call an "oyster relay"—may be just as effective and much cheaper than other PHP methods, which they say are "expensive, capital intensive, difficult to use with large numbers of oysters, or not readily available."
During their study—funded by Virginia Sea Grant's Fishery Resource Grant Program—the team moved farmed oysters from one relatively low- and two moderate-salinity sites in Chesapeake Bay (the Coan River, the York River, and Nassawadox Creek) to Little Machipongo Inlet on the seaside of Virginia's Eastern Shore, where waters are close to full ocean salinity. They moved about 200 oysters from each site, carrying them by truck in insulated coolers.
The team ran two experiments, one beginning in mid-August 2010 and the other in mid-September. Both dates lie within the FDA's 2010 "risk season," which roughly coincides with the adage that raw oysters shouldn't be consumed in months without an "r." The team sampled the transplanted oysters upon collection, after one week, and again after two weeks, using molecular diagnostics to measure levels of Vibrio vulnificus in oyster tissues.
Their findings, say Reece, "clearly show that high-salinity relay is a potentially viable method to reduce Vibrio in oysters grown and harvested in Virginia."
Their molecular studies, measured by the "most probable number" (MPN) of Vibrio vulnificus bacteria in each sample, shows that exposure to salty water decreased Vibrio vulnificus levels from a high of 750 MPN per gram of meat in pre-transplant oysters (with an average of 160 MPN per gram) to less than 1 MPN per gram. The team also found that the shift from fresher to saltier water has little effect on oyster health, with less than 5% mortality even among the oysters experiencing the largest salinity change.
Another important outcome of the study was initial confirmation that a novel part of the team's research—use of a real-time quantitative polymerase chain reaction (qPCR) assay—worked well to identify Vibrio vulnificus.
The team cautions that further study with a larger number of more highly infected oysters is needed to confirm that an oyster relay can effectively bring Vibrio to the level (less than 30 MPN per gram) required by the Interstate Shellfish Sanitation Conference. The ISSC—a partnership of state and federal control agencies, the shellfish industry, and the academic community—sets the sanitation guidelines that regulate the harvesting, processing, and shipping of U.S. shellfish.
David Malmquist | EurekAlert!
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy