UNH Researchers Hone In On Harmful Oyster Bacteria

May 11, 2015

Researchers at the University of New Hampshire have discovered a new way to detect a bacterium that has contaminated New England oyster beds and made some consumers sick. Dr. Cheryl Whistler is an associate professor of molecular, cellular, and biomedical sciences at UNH and one of the co-developers of this new detection method. She spoke with NHPR's Peter Biello. 

What bacterium does this detect?

 It detects vibrio parahaemolyticus. That’s a hard one to say, so we can just call it V. Para.

What kind of harm does this bacterium do?

It is the leading cause of bacterial seafood-borne infections in the world. It causes a severe gastroenteritis. It rarely leads to death, but it can in some cases lead to a fatal sepsis. But typically  people just feel like they’re going to die because they’re just so ill before it clears.

Is this a naturally occurring bacteria?

It is absolutely a naturally occurring bacteria. And the vast majority of the strains out in estuaries are actually harmless and don’t cause any kind of human infection. And it’s really very rare that a strain is capable of causing an infection in humans.

Does infection happen because people eat oysters raw?

Yes, indeed. So V. Para cannot infect if it’s been killed. And if you cook the shellfish, you are actually entirely safe, as long as there is no cross contamination from mishandling.

What is the new method of detection?

It’s based on a platform that is being used for other detections. It’s called PCR, or polymerase chain reaction. What we’ve done that’s different than others is we’ve actually sequenced the genomes of hundreds of strains and done detailed comparisons of their genomic content, so the genes they actually have. And we’ve identified particularly diagnostic traits in this particular strain that’s become invasive in the Atlantic ocean. And we developed that strategy to detect that strain and the known virulence genes that contribute to disease. So it’s a multi-locus detection strategy.

And it would allow a sample to be taken from a particular oyster bed. And you can test that sample to see if the bacterium exists.

Yes, so we can enumerate the bacterium through standard practices, applying this detection strategy on top of what scientists already to do, or managers do, actually enumerate bacteria in oyster beds. But it can also be used if somebody becomes ill. We can test the strain that comes from the human very rapidly and know whether or not we have an emerging outbreak by this particularly invasive strain.

So now that you can detect it, is it also easier to destroy it?

I will say that our primary concern is management because, unless you cook it, you can’t stop infection. There’s always going to be some risk with eating raw shellfish, but of course raw shellfish is delicious, so we would really want to be able to use this detection to inform management strategies on how quickly the shellfish is actually iced so there’s no growth of bacteria. Its presence alone is not so much the issue as its concentration becoming high enough that it can cause a human infection, because these bacteria don’t typically cause infection when they’re in very low concentration in the shellfish. We really need to inform proper management, so that when these bacteria emerge and start becoming very abundant, that’s when you would want to monitor the shellfish harvesting, do some proactive closures during windows when we know it’s very abundant, but also be able to make decisions on reopening the harvesting when the time has passed and it’s safe to eat the shellfish again.

Will this prevent losses for oyster harvesters?

Absolutely. And the reputation of oyster farms is incredibly important. So if they are providing a safe product, and they’re doing everything they can to ensure the safety of the product, the product is going to maintain its market share. It’s really when you have unexpected infections and the negative press that comes along with that that is really harmful to the growers, because they really are doing an incredible job of managing their harvesting, but we really need to have good scientific information to help people make decisions about what are the appropriate measures to take to ensure public health.