Spotlighting Unsafe Shellfish

Seafood contaminated by “red tides” and other toxic algae is hazardous to eat, often producing gastrointestinal problems and other symptoms, but it’s difficult to differentiate a contaminated batch of seafood from one that is free of such toxins. Now, a new marker developed by chemists at the University of California, San Diego (UCSD) makes it easier to see if shellfish are filled with toxin-producing organisms (Reyes CP, La Clair JJ, Burkart MD, Chem Commun. 2010;46:8151-8153).

While filtering seawater for food, shellfish like mussels and oysters accumulate single-celled marine organisms called dinoflagellates in their digestive systems. Although these creatures are usually harmless, sometimes they harbor hazardous toxins. While studying the dinoflagellates, UCSD chemistry professor Michael Burkart, PhD, and colleagues discovered they could use a chemical tag, visible under a fluorescence microscope, to highlight bacteria in the organisms.

“First, we cultured live shellfish in toxic dinoflagellates; then we cultured others in a sample of dinoflagellates that do not make the toxin,” he said. “We then excised the stomach, added our dye to the liquid, and put the liquid under the microscope. And the assay proved accurate: If you see the little bright dots under a fluorescent microscope, that’s a contaminated batch of shellfish.” And when the chemists added antibiotics to the mix, the fluorescent lights quickly switched off again, heralding the elimination of the contaminants.

According to Dr. Burkart, this type of assay isn’t familiar ground for many aquaculture facilities. “The existing assays for this kind of contamination are pretty poor,” he said. “The ones I’m familiar with involve injecting muscle meat into mice and seeing if the mice get sick. Some in vitro assays let you look at enzyme activities, but they’re slow and not that effective.” And although fluorescence microscopes are expensive, Dr. Burkart noted that rapidly developing technology may soon make the tag easy to detect with a handheld device–yes, you may soon have the option to turn your iPhone into a fluorescence microscope.