Vibrios and Human Health

Most people can consume oysters by the dozens without ill effect, but people with liver disorders, diabetes, and immune-compromising conditions such as HIV/AIDS are at risk for the deadly vibriosis illness caused by a species of Vibrio. Individuals who take prescribed medication to decrease stomach acid or who have had gastric surgery are also at risk.

Vibrio vulnificus, a gram-negative bacteria that occurs naturally, especially in brackish, warm coastal Gulf of Mexico waters, causes a particularly horrific illness in vulnerable individuals—and the mortality rate hovers at 50 percent. Some 95 percent of all seafood-related deaths in the U.S. are caused by V. vulnificus, and the CDC reports that from 1996 till 2006, Vibrio infections increased by 78 percent.

The obvious solution to the problem would seem to be educating at-risk oyster eaters about the danger they’re courting. The Interstate Shellfish Sanitation Conference—a coalition of shellfish industry members and state and federal regulatory agencies—launched an expensive information campaign aimed at doctors and restaurants with the idea of educating high-risk individuals about the dangers of eating raw or undercooked oysters.

It didn’t work. Apparently, those who love the briny taste of raw live oysters are willing to take the risk.

In 2009, FDA proposed requiring all oyster producers to use a form of Post Harvest Processing (PHP) to sterilize raw oysters. The seafood industry pushed back, insisting that requiring PHP processes would drive many seafood companies out of business. That warning is not unrealistic because oyster harvesters are already under siege as a result of man’s degradation of the Gulf coastal environment and scourges like the oyster drill, a carnivorous marine snail that drills a hole in an oyster’s shell and sucks out the sweet innards.

Most oyster harvesters are small family operations, and they’ve already been decimated by oil spills in the Gulf. The nation’s richest oyster grounds have also been affected by a series of hurricanes lashing the region and flooding from the Mississippi River, which flushed a torrent of fresh water into the northern Gulf, reducing salinity. More recently, the Deepwater Horizon oil spill tainted the brand name “Gulf Seafood,” despite all the testing conducted by state and federal agencies that deemed seafood from the affected areas safe.

The FDA’s plan would have required all oysters harvested from the Gulf of Mexico between May and October to be processed. PHP, however, not only kills oysters—changing their taste and texture—it is expensive for small operations. Most don’t have the necessary capital to buy the equipment necessary to meet the proposed FDA regulations.

Avery Bates, vice president of the Organized Seafood Association-Alabama, told the Associated Press that two-thirds of Alabama’s 50 “mom-and-pop” oyster shops would close because of the costs associated with processing the oysters.

Is there a way to make eating oysters safer without decimating a struggling mom-and-pop oyster industry? Unexpectedly, research conducted in my lab at Auburn University could become central to the debate.

Depuration

Since 2007, Auburn has been studying a post-harvest process called depuration to eliminate Vibrio vulnificus from Gulf oysters. Depuration involves transferring shellfish from polluted waters to a controlled, cleaner aquatic environment, allowing then to “open” and eliminate contaminants themselves, thus reducing bacteria to low levels.

Mollusk depuration is common in Europe, where the process is used to eliminate microbes that proliferate in waters contaminated by fecal waste.

In the U.S., depuration systems must be approved by the FDA and are used only in Massachusetts (clams), Maine (clams and oysters), and Florida (clams). These depuration systems are utilized only in fecal-contaminated waters because depuration of pathogens that occur naturally, such as vibrios, has proven challenging.