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Drug Residues in Imported
Seafood and Food Safety
Authored by Dr. Kim W. Baughman, Director of Development, Microbac Laboratories, Inc. One of the major food safety concerns of the FDA is the presence of unapproved
antibiotics and antifungal chemicals in imported seafood
. This is of particular concern
because consumption of seafood has continued to increase to the point where currently,
more than 75% of the seafood consumed in the United States is imported and almost 50%
is farm-raised (aquacultured). The FDA has found evidence that several unapproved
antibiotics have been used in aquaculture in some countries. Since 2007, they have taken
specific action against seafood imported from China. Several seafood products from
China have been placed on automatic detention, meaning they are held at the port until
testing data clear them. Enforcement is focusing on several classes of compounds that are
not approved for food-producing animals.
Nitrofurans are a broad group of synthetic antibiotics characterized by the Nitrofuran
ring in their structure and by their effectiveness against bacteria. The most widely used
nitrofurans are furazolidone, furaltadone, nitrofurazone, and nitrofurantoin. In the tissue,
these compounds metabolize to 3-amino-2-oxazolidinone (AOZ), 3-amino-5-
methylmorpholino-2-oxazolidinone (AMOZ), semicarbazide (SEM), and 1-
aminohydantoin (AHD). Detection of nitrofurans is based on the determination of the
metabolites. The FDA banned their use in food-producing animals in 2002, but residues
continue to be found in imported shrimp.
Malachite Green is still used in home aquariums because of its antifungal properties, but
it is banned in aquaculture in the United States, EU, and Canada. Malachite green
metabolizes to Leucomalachite green upon absorption into the tissue, thus the analytical
method must determine both compounds to detect its use in aquaculture. Malachite green
has been detected by the FDA in imported eel and several species of imported fish.
Crystal Violet, also referred to as gentian violet, is another powerful antifungal agent. It
has been used in the aquaculture industry for treatment and prevention of external fungal
and parasitic infections in fish and fish eggs. It also converts to the leuco form,
Leucocrystal violet, upon absorption in the tissue of fish. It accumulates in the muscle
tissue and is eliminated very slowly. It has been detected in imported fish and shrimp.
Quinolones and Fluoroquinolones are a class of synthetic antibacterial drugs that work
by interfering with the ability of the bacteria DNA to replicate. Numerous compounds
have been developed, but the most common are the fluoroquinolones: Enrofloxacin
(ENRO), Ciprofloxacin (CIPRO), Difloxacin (DIFLOX), and Sarafloxacin (SARA).
Testing is also conducted for certain quinolones, including Flumequine and Oxolinic
acid. These compounds have been found in several species of imported fish.
2011 Microbac Laboratories, Inc.
Drug Residues in Imported
Seafood and Food Safety
Chloramphenicol is a bacteriostatic compound, interfering with the protein synthesis of
bacterial protein, first isolated in 1947 from Streptomyces venezuelae. It is not approved
for use in food-producing animals, but has been detected in imported shrimp crayfish and
Chemical Analysis of Aquaculture Drug Residues
Several methods have been developed recently for aquaculture drug residues. The best and most sensitive use a high-performance liquid chromatograph interfaced to tandem mass spectrometers, (LC-mass-spec-mass-spec or LC/MS/MS). This instrument significantly reduces the background signal and, therefore, allows the measurement of organic compounds at very low levels, in the parts-per- trillion range, for many compounds. The FDA has published requirements for sampling and testing of detained products and these should be consulted for specific guidance. For most products, a minimum of 12 sub-samples are to be collected and submitted. For most of the residues, the sub-samples are composited at the laboratory and analyzed as a single sample, however, in the case of nitrofurans in shrimp, the 12 samples are analyzed separately. Microbac Laboratories, Inc. performs a broad range of food safety testing, including
LC/MS/MS analysis for all of these aquaculture drug residues.
For more information, please contact: [email protected] 2011 Microbac Laboratories, Inc.



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