Pathogen contaminating seafood identified by researchers

By Joseph James Whitworth

- Last updated on GMT

Picture: iStock
Picture: iStock

Related tags Tuna

A new strain of a bacterial pathogen that has contaminated seafood and sickened shellfish consumers has been identified by researchers.

University of New Hampshire scientists did the work with the Food and Drug Administration and public health and shellfish management agencies in five states.

They discovered a Vibrio parahaemolyticus strain​ identified as ST631 is predominantly endemic to the Atlantic Coast of North America and has been traced to shellfish harvested in seven Atlantic coastal states and Canada.

From harmless to pathogenic

ST631 is the second most prevalent strain isolated from patients sickened by product from the Northeast US.

“We identified this strain nearly ten years ago in New Hampshire where there have been no reported shellfish-borne infections, and more than five years ago from clinical sources from Massachusetts so we knew it was a potential problem in this region​,” said Cheryl Whistler, associate professor of molecular, cellular, and biomedical sciences at UNH.

“We were surprised to learn that it was so widespread and that it could thrive in such contrasting water temperatures as would be found in Florida compared to Prince Edward Island and the Gulf of Maine.”

Vibrio parahaemolyticus is the leading seafood-transmitted bacterial pathogen globally with an estimated 45,000 infections in the US every year, according to the Centers for Disease Control and Prevention.

UNH researchers and collaborators will develop quantitative methods for detecting this strain in the environment and attempt to understand how it evolved from harmless to pathogenic.

They can also now monitor its presence spread and potentially reduce infections.

In 2015 UNH scientists invented a method to detect specific Vibrio parahaemolyticus strains that cause human illness in New England oyster beds, including ST631 and ST36.

The patent-pending detection method identifies shellfish harboring disease-carrying strains of Vibrio parahaemolyticus.

Fishy findings

Meanwhile, a study from researchers at UCLA and Loyola Marymount University​ found almost half of sushi was mislabeled.

They checked the DNA of fish ordered at 26 Los Angeles sushi restaurants from 2012 through 2015, and found that 47% percent of sushi was affected.

Sushi represented as tuna was almost always that and salmon was mislabeled about one in 10 times.

But out of 43 orders of halibut and 32 of red snapper, DNA tests showed a different kind of fish.

A one-year sampling of grocery stores found similar rates, suggesting the bait-and-switch may occur earlier in the supply chain than the point of sale to consumers, said the study.

Paul Barber, a UCLA professor of ecology and evolutionary biology and senior author of the study, said: “Fish fraud could be accidental, but I suspect that in some cases the mislabeling is very much intentional, though it’s hard to know where in the supply chain it begins.

“I suspected we would find some mislabeling, but I didn’t think it would be as high as we found in some species.”

Researcher said fraud undermines environmental regulations limiting overfishing, introduces unexpected health risks and interferes with consumers’ decisions.

While only one of 48 samples was not tuna, two were Atlantic bluefin tuna and southern bluefin tuna, species classified as endangered and critically endangered.

Demian Willette, lead author, said DNA barcoding is becoming an increasingly popular tool to identify mislabeled products.

“Our finding of a persistently high rate of seafood mislabeling should encourage consumers to demand strong truth-in-menu laws from local public health agencies. Citizen-science and crowd-sourced data also have real potential to keep the consumer informed.”

The researchers did not name the sushi restaurants.

Barber said the goal was not to point fingers but to make people aware of the larger issue.

“I think it would be really cool to work with some restaurants to test their shipments so we can start to work out where in the supply chain the fraud is taking place. I would love to know what the restaurants think they’re getting from the suppliers.”

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