Phage-based Detection Systems. Phages are viruses that can infect bacteria, Dr. Vongkamjan notes. “Wide-range applications of phages have been reported, including as pathogen detection systems,” she says. “Phages are typically modified to carry a gene such as a luciferase that encodes a protein, allowing for its rapid or easy detection. A real-time light emission produced by luciferase in the infected pathogen, such as Listeria, can be detected.”
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Biosensor-based Methods. Biosensors are devices used to detect biological analytes, such as pathogens, according to Jane Ru Choi, PhD, a postdoctoral fellow in biomedical engineering at the University of British Columbia, Vancouver, Canada.
“These devices are named based on their detection approaches, such as colorimetric, fluorescent, electrochemical, and chemiluminescent-based biosensors,” Dr. Choi relates. “Biosensors can be implemented in point-of-care (POC) devices, which are diagnostic tools used to obtain results quickly close to the subject of the test.
With advances in POC testing, scientists have developed microfluidic chip-based devices including paper-based devices, such as lateral flow test strips and three-dimensional paper-based microfluidic devices, Dr. Choi says. Both microfluidic chip-based and paper-based devices can employ colorimetric, fluorescent, chemiluminescent, and chemiluminescent-based approaches, she elaborates.
“Despite some limitations, including poor sensitivity and lack of quantification, these emerging technologies are fast gaining popularity for use in detecting food contaminants, including those in seafood,” Dr. Choi points out. “POCs offer numerous advantages, including being affordable, sensitive, specific, user-friendly, rapid and robust, equipment free, and deliverable to end users.”
Certified Laboratories, Inc., based in Melville, N.Y., typically uses ribotyping for pathogen “fingerprinting” in seafood, according to Martin Mitchell, Certified’s chairman emeritus.
“Ribotyping is a molecular technique that capitalizes on unique genomic structures to differentiate strains of the pathogen,” Mitchell relates. “Ribotyping offers the benefits of molecular biology at less cost than whole-genome sequencing (WGS).
“Ribotyping and WGS refer to two specific techniques that fall under the broader term of “strain typing,” Mitchell continues. “Strain typing is any technique used to differentiate or determine the commonality of one strain of organism from another.”
According to Mitchell, strain typing is a useful tool for environmental monitoring in seafood processing establishments. “If, for example, sanitation is not effective in removing Listeria from a plant, strain typing can be used to determine if the organism came in on raw product, or if there are harborage issues in the facility,” he explains. “If the specific Listeria organism identified after sanitation is the same as the one identified before sanitation, that’s an indication there is a harborage issue.”
Supporting the U.S. Seafood Inspection Program
Fish and seafood products testing is conducted by the National Seafood Inspection Laboratory (NSIL), Pascagoula, Miss., to support the U.S. Department of Commerce Seafood Inspection Program through the NOAA National Marine Fisheries Service (NMFS), according to Jon Bell, PhD, NSIL director. “NOAA’s Office of International Affairs and Seafood Inspection (OIASI) is the U.S. competent export certification authority for fish and fisheries products,” Dr. Bell relates.
The NSIL supports the Seafood Commerce and Certification Division of the OIASI by verifying that U.S. exports meet importing governments’ food safety requirements, Dr. Bell notes. The verification process includes pathogen and indicator organism testing, along with processing audits conducted by the OIASI Seafood Inspection Program (SIP), he says.
“We conduct microbiological analyses on fish and fishery products for human consumption and aquatic fisheries byproducts to be used as ingredients in animal feeds and pet foods,” Dr. Bell elaborates. “We test for a number of microbiological contaminants, including Listeria, Salmonella, Staphylococcus aureus, fecal coliforms, and Vibrio bacteria, among others.”
“We also test for hazards in finished ready-to-eat seafood products, including cooked, packaged, vacuum packed, and frozen items,” adds Angela Ruple, MS, NSIL supervising lead analyst.