Sea Briefs is a report on the results of the Mississippi-Alabama Sea Grant Consortium.
Editor: Melissa Schneider
is available in PDF format from:
MASGC supports applied, interdisciplinary marine science research, education and outreach efforts to foster the sustainable development and management of the Mississippi and Alabama coasts and nearshore ecosystems of the Gulf of Mexico
If you’re a shellfish lover, Vibrio vulnificus is one of the bad guys.
This bacterium can cause significant harm or even death if consumed or otherwise introduced into the body. Raw oysters are one of the most common sources of Vibrio infection, responsible for over 95 percent of all seafood-related deaths. Some scientists are out to make oysters safer through Mississippi-Alabama Sea Grant funded research.
Asim K. Bej, a biology professor at The University of Alabama at Birmingham, is working on a method of detecting Vibrio vulnificus in post-harvest treated shellfish. The current DNA-based detection method involves making many copies (amplification) of a targeted gene of a bacterium via polymerase chain reaction (PCR), first developed in the mid-1980s. Bej’s method uses the basic principle of PCR, but a much simpler and cost-effective approach of the amplification of a gene at an isothermal condition. Nucleic acid carries the genetic information specific for a pathogen, and isothermal amplification makes the specific genetic signature more readily identifiable. Typical PCR involves alternating the temperature between heat and cold many times by using a relatively expensive thermal cycler, but Bej’s method is performed in a single tube at a constant temperature. Positive amplification of the targeted gene, which indicates the presence of the bacterium V. vulnificus, is determined by using a simple disposable colorimetric device. The process is easy to perform and does not require rigorous training of personnel.
Bej’s hope is that this simple and powerful emerging technology will be adopted by the shellfish industry and biotech companies.
Although many detection methods never see use beyond the lab where they are developed, Bej has a reputation for being on the cutting edge, according to Andy DePaola, a microbiologist with the U.S. Food and Drug Administration’s Gulf Coast Seafood Laboratory. Agencies, such as the FDA and the U.S. Centers for Disease Control use many of Bej’s previously developed methods for the detection of vibrios. One advantage of the isothermal amplification over real-time PCR is that it is less expensive, DePaola said.
Of course, detecting the Vibrio vulnificus bacterium is only the first step.
Professor Mark T. Hamann, Research Scientist Jiangnan Peng and Ph.D. student Damaris Meujo, all of The University of Mississippi, have developed a technique that harnesses pressurized carbon dioxide to reduce or eliminate Vibrio concentrations in oysters. Oysters are placed in a sterilized chamber and submersed in super-critical carbon dioxide (carbon dioxide at temperature and pressure above its critical point). Studies have indicated that super-critical carbon dioxide possesses the ability to kill bacteria.
A super-critical fluid behaves much like a gas and a liquid. A solvent at this gas/liquid stage can flow more freely through solid materials. This process is used on a large scale to decaffeinate coffee, and Hamann’s group has shown it could be used to control bacterial levels in seafood.
The Vibrio bacteria can be reduced to acceptable levels or even completely eliminated by subjecting oysters to specific temperatures and pressure for a specific length of time. Because the method is not pharmacologically targeted like an antibiotic, the approach can be used to kill virtually any bacteria, fungi or parasite.
The treatment causes little or no change to the oysters, depending on the level of exposure to carbon dioxide. Post-treatment tests indicate that treated oysters differ slightly, if at all, in appearance, and there is no difference in taste, Hamann said.
He is optimistic that this system may be used to treat other types of seafood and could be instrumental in reducing methylmercury levels in certain seafood.
The process is environmentally benign, highly functional, scalable and provides opportunities to process foods without a dramatic change to quality.