Very Serious Superbugs in Imported Seafood

Image: Matsuyuki, Flickr

Image: Matsuyuki/ Flickr

Breaking news today from the Centers for Disease Control and Prevention, out of its open-access journal Emerging Infectious Diseases: Researchers in Canada have identified a very highly resistant bacterium in squid imported from South Korea and being sold in a Chinese grocery store.

The letter reporting the finding was supposed to go live at noon ET, but hasn’t yet. When it does, it will be linked from this page, under the subheading Letters. It is titled: “Carbapenamase-Producing Organism in Food, 2014.”

The letter, signed by Joseph E. Rubin, Samantha Ekanayake and Champika Fernando of the University of Saskatchewan, reports that, in the squid, they found a variety of a common bacterium, Pseudomonas, carrying a gene that directs production of an enzyme called VIM-2 carbapenemase. It’s the “carbapenemase” that is the troubling factor here. Carbapenems are the truly last of the few remaining last-resort antibiotics in the world. The global advance of carbapenem resistance — via superbugs such as NDM from Asia, and OXA and VIM primarily from southern Europe — is what the CDC’s director was talking about last year when he referred to the worldwide threat from “nightmare bacteria.” 

Most of the spread of carbapenem resistance has been through people, who picked it up in a hospital or acquired it accidentally from contaminated water, especially in south Asia. But because carbapenem resistance largely travels via gut bacteria, some microbiologists have been apprehensive that it might get into the food chain. After all, many common foodborne diseases arrive via what’s politely called the “fecal-oral route” — which is to say, fecal bacteria got on the food you eat. Since some of those bacteria, such as E. coli, are known to carry NDM and the other carbapenemases, it made sense to wonder whether food could transmit them also. It’s an especially important question because the government surveillance programs that look for resistant bacteria on food are limited in the geographical sites, types of food, and types of bacteria they look for — so the possibility has always existed that something could sneak through.

Which the authors say they were worried about. From their letter:

…the scope of antimicrobial drug resistance surveillance programs is limited to major agricultural products (poultry, beef, and pork). In our modern, ethnically diverse societies, niche-market meat products, including imported foods, are becoming increasingly common. Worldwide dissemination of the Klebsiella pneumoniae, VIM, OXA, and New Delhi metallo-b-lactamase type carbapenemases among humans has been facilitated by intercontinental passenger travel, but the role of the global food trade in this dissemination has not been investigated…

Among other items, the squid was purchased from a Chinese grocery store in Saskatoon, Canada, in January 2014 as part of a drug-resistance surveillance pilot study. Although no country-of-origin labeling was available for inspection, the store owner reported that, according to the distributor, this squid originated in South Korea.

Beyond the obvious, that this is a first finding of a resistance factor where it has not previously been, here are some concerns: Because the carbapenem-resistant bacteria tend to be gut bacteria, anything that conducts them into your gut—like, for instance, swallowing them—is problematic. The issue isn’t that the bacterium is going to cause a foodborne illness immediately; the bacteria carrying this gene was not a disease-causing variety. Rather, the concern is that the DNA conferring this resistance passes from this bacterium into the vast colony of diverse bacteria that live in your gut for your entire life, becoming incorporated into your gut flora and posing a risk of drug-resistant illness at some future point when the balance of your immune system slips.

That this was found on seafood—a type of food that we tend to undercook and sometimes eat raw—just increases the risk of transmission. And that’s not even to mention the possibility that bacteria containing the gene spread to other seafood or other foods in that store, or in the kitchens of anyone unlucky enough to bring them home.

As the authors state:

The presence of carbapenemase-producing organisms in the food supply is alarming… There is an urgent need for expanded resistance surveillance for carbapenemase-producing organisms and their resistance plasmids in food products that are not captured under current programs.



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