Farmed fish are given antibiotics to fight disease and some trace elements of these end up in the seafood we eat, but a new study confirms there may be less than thought, depending on the species, or region of the globe the product is raised.
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, the United States 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 weren't too surprised [when there weren't] because antibiotics don't stay in the fish all that long. There is supposed to be a period of time between when they administer antibiotics and when the fish is processed.”
However, regulations in this area vary between countries.
“It was a small study so we couldn't really say what the regulations were in each country,” she explained. “We hope to do larger samples in the future. This was just a few grocery stores that we sampled.”
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.
President Obama proposed the first governmental steps to address the problem in September, establishing a task-force, including representatives from the departments of health, defense and agriculture.
The effort was praised by many, though some think much more needs to be done to control the largest consumers of antibiotics—animals farmed for human consumption.
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.
The study represents the first to evaluate previously unmonitored antibiotics and the largest reconnaissance conducted to date on antibiotics present in seafood. The problem is not the antibiotics themselves but how their overuse can induce microbes to evade immune response or develop drug resistance over time, running the risk of producing multi-drug resistant and more powerful drug resistant strains that are more difficult to kill.
To evaluate the extent of the problem of antibiotics overuse in aquaculture, the National Oceanic and Atmospheric Administration (NOAA) researchers studied 27 samples of farmed seafood sold at grocery stores in Arizona and California.The samples represent five of the top ten most consumed seafood varieties in the U.S.: 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. Researchers were surprised when they detected this antibiotic in wild-caught shrimp from Mexico, which they suggest may be due to mislabeling, coastal pollution, from sewage contamination, or cross-contamination during handling and processing.
All seafood analyzed was found to be in compliance with U.S. 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 (such as amoxicillin and ampicillin) used in aquaculture are also used in human medicine, 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.
The development and spread of antibiotic resistance is a public health priority that is divorced from the regulatory limits designed to prevent adverse outcomes from human ingestion of drugs, concluded the authors of the study.
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.
In related news covered by ANA, and in other reports, there’s been some recent research done on the use of probiotics—essentially living microorganisms which when administered in adequate amounts confer a health benefit on the host—to fight pathogens in shellfish and finfish, but more needs to be done to isolate, research, and manufacture probiotic medicine before these can be implemented commercially in the industry, experts said.
– 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
NOTE: Antibiotic Use in Salmon Net-Pen Culture
According to a recently published paper by the National Oceanic and Atmospheric Administration (NOAA), antibiotic use in the salmon net-pen aquaculture industry has dropped in the past 20 years. In Norway, antibiotic use has decreased 95% in the past 20 years because of the introduction and use of more efficacious vaccines.
The recent paper, titled Environmental Performance of Marine Net-Pen Aquaculture in the United States, also reported similar declines in British Columbia and the U.S.A., where three antibiotics are approved and labeled to treat specific diseases in specific aquatic species. The majority of these labels are for freshwater applications. Any use by species, conditions, or diseases other than those listed on the label must be done via extra-label use that requires a licensed veterinarian to approve, according to NOAA.
As in Norway, effective vaccines have significantly reduced the use of antibiotics use in U.S. salmon farming. In Maine, no antibiotics use was recorded in net-pen salmon farms starting from 2007 to 2012 - the last year records are available.
This contrasts with approximately 13,500 metric tons of antibiotics being used in 2010 for all animals sourced for human consumption, according to the United States Food and Drug Administration.
Reference: Michael B. Rust, Kevin H. Amos, April L. Bagwill, Walton W. Dickhoff, Lorenzo M. Juarez, Carol S. Price, James A. Morris Jr. & Michael C. Rubino. 2014. Fisheries Vol 39, Issue 11, pages 508-524 http://www.tandfonline.com/doi/full/10.1080/03632415.2014.966818#tabModule