Few antibiotics found in marketed seafood

Erich Luening
March 26, 2015
By Erich Luening

Farmed fish are given antibiotics to fight disease and some trace elements of those end up in seafood we eat at the dinner table, but a new study finds there may be less than otherwise thought, depending on the species, or region of the globe the product is raised, according to a new study.

            Researchers at the Arizona State University’s Biodesign Institute examined antibiotic use in shrimp, salmon, catfish, trout, tilapia and swai, originating from 11 countries. Of the 47 antibiotics evaluated, researchers discovered traces of just five. The fish were sourced from Bangladesh, Canada, Chile, China, Indonesia, Mexico, Panama, Scotland, Thailand, US and Vietnam. No evaluation of the comparable regulations were made as part of this study, but the authors said that might be included in a more comprehensive analysis.

            “Five antibiotics showed up,” co-author of the study and PhD candidate Hamsa Done told Aquaculture North America. “We hypothesized that there would be more but not too surprised because the antibiotics don't stay in fish all that long. There is supposed to be a period of time between when they administer antibiotics and when the fish is processed.”

            She said there is more work to be done in this area as the aquaculture industry grows and the menace of germs acquiring resistance to antibiotics overused in several sectors, including human and animal health.

The problem

            The other co-author of the recent study, Rolf Halden, PhD, in a statement releasing the study said the threat of living in a post-antibiotic era can’t be avoided without revising current practices in the use of such medicines in animal husbandry, including aquaculture.

            The study, titled “Reconnaissance of 47 antibiotics and associated microbial risks in seafood sold in the United States,” examined the persistence of antibiotics in seafood raised by modern aquaculture practices. The area is relatively unexplored, as the focus of other studies have been on drugs used in human medicine.

           To evaluate how bad the problem of antibiotics overuse in aquaculture may be, researchers studied 27 samples of farmed seafood sold at grocery stores in Arizona and California, purchased by the National Oceanic and Atmospheric Administration (NOAA).The samples represent the five of the top ten most consumed seafood varieties in the US: shrimp, tilapia, catfish, swai, and Atlantic salmon.

            The five antibiotics that showed up in detectable amounts were: oxytetracycline in farmed tilapia, salmon and trout, as well as in wild shrimp; 4-epioxytetracycline in farmed salmon; sulfadimethoxine in farmed shrimp, ormetoprim in farmed salmon, and virginiamycin in farmed salmon that had even been marked as antibiotic-free, according to the study.

            Oxytetracycline, the most commonly used antibiotic in aquaculture, was the most prevalent in the samples.

            However, all seafood analyzed was found to be in compliance with US Food and Drug Administration (FDA) regulations. However, the authors note that sub-regulatory antibiotic levels can promote resistance development in microbes, according to existing meta-analysis previous studies.

Further research needed

            Because many antibiotics used in aquaculture are also used in human medicine, like amoxicillin and ampicillin, proper monitoring of antibiotic residues in seafood is critical, the authors point out.

            The trend in the last three decades of notable increases in the number of drug resistant strains identified in seafood is of concern, the authors concluded. Monitoring studies like this one are just one of multiple steps required to understand and manage potential risks posed by the overuse of antibiotics in aquaculture and society on the whole.

            Future studies are warranted to fully understand the connection between aquaculture use of antibiotics, development of drug resistance, human exposure to resistant pathogens, and ensuing morbidity and mortality in seafood consumers.

— Erich Luening

Reference: H.Y. Done, R.U. Halden. 2014. Reconnaissance of 47 antibiotics and associated microbial risks in seafood sold in the United States, J. Hazard. Mater. http://dx.doi.org/10.1016/j.jhazmat.2014.08.075.

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