Seafood Safety: New Technologies and International Collaborations Improve Pathogen Testing

Seafood is a whale of an industry throughout the world.

Fish consumption grew from 19.8 pounds per capita in 1961 to 44.5 pounds in 2015, at an average rate of about 1.5 percent per year, according to a 2018 report from the Food and Agriculture Organization of the United Nations (FAO). Preliminary estimates for 2016 and 2017 point to further growth to about 44.75 pounds and 45.2 pounds, respectively, FAO projects.

Estimated U.S. per capita consumption of fish and shellfish was 16.0 pounds in 2017, an increase of 1.1 pounds from the 14.9 pounds consumed in 2016, according to the National Oceanic and Atmospheric Administration (NOAA).

Not surprisingly, pathogen control and testing of seafood for microbiological hazards is an issue of ever-increasing importance.

In 2019 the FDA published its Evaluation of the Seafood HACCP Program for Fiscal Years 2006-2014. Presenting data from actual inspections, the report states, “The success rates for having and implementing HACCP (Hazard Analysis and Critical Control Points) plan controls for the hazards of pathogen growth/toxin formation and scombrotoxin were noticeably less than those for the other hazards.”

Prominent Seafood Pathogens

Foodborne pathogens typically associated with seafood products and seafood processing plant environments include Vibrio vulnificus, Vibrio parahaemolyticus, Salmonella spp., and Listeria monocytogenes, according to Kitiya Vongkamjan, PhD, an assistant professor in the Department of Food Technology at Prince of Songkla University in Hat Yai, Thailand.

Dr. Vongkamjan says the various rapid technologies available for detection of these pathogens offer several benefits, including:

• determination of specific pathogens in raw materials, finished products, and environmental samples
• detection of low numbers of pathogens in complex matrices of organic materials that are loaded with non-pathogenic microorganisms
• monitoring of process control, cleaning and hygienic practices during manufacture
• time, labor, and expense savings

“In contrast to conventional methods, rapid detection enables generation of fast and reliable results, which is especially important in light of ever-increasing global seafood trade requiring rapid transport over vast distances,” Dr. Vongkamjan relates.

Rapid detection methods can be categorized into nucleic acid-based, antigen-antibody based, biosensor-based, and phage-based methods, Dr. Vongkamjan notes.

Nucleic Acid-based Methods. Scientists have developed nucleic acid-based methods for detection and identification of specific DNA or RNA sequence of the target pathogen, Dr. Vongkamjan says. “Detection of a target nucleic acid sequence is performed by simple polymerase chain reaction (PCR), hybridization probes, or primers,” she elaborates. “Nucleic-acid based methods detect specific genes in the target pathogens associated with seafood.”

PCR-based methods are often classified into conventional PCR and real-time/quantitative PCR (qPCR), Dr. Vongkamjan explains. “Real-time PCR combines the specificity of conventional PCR with the quantitative measurement of fluorescence for monitoring amplification of specific genes in the target pathogens,” she explains. “A number of qPCR schemes have been designed to detect target genes such as the cholera toxin gene (ctxA) of V. cholerae or the tdh/trh genes of V. parahaemolyticus in fish and crustacean samples. Detection of multiple target genes of different species, serotype, or subtypes can be done in a single reaction by multiplex assay.”

Loop-mediated isothermal amplification (LAMP) is another variant of nucleic acid-based methods, Dr. Vongkamjan continues. “Most LAMP-based assays have been used for detection of V. parahaemolyticus, V. vulnificus, Salmonella spp., and L. monocytogenes in seafood and environmental samples. LAMP is proven to be more specific and sensitive compared to the other PCR-based assays for the detection of foodborne pathogens.”

Antibody-based Methods. Antibody-based detection relies on a highly specific and sensitive antibody-based system for the antigen present on the target pathogen, Dr. Vongkamjan says. “Most antigens contain amino acid sequences that are distinguishable among the target pathogens and other related non-target organisms,” she relates. “This specificity allows strong reactivity of antibody to the antigen in the target pathogen. Enzyme-linked immunosorbent assay is one such standard pathogen detection tool, whose detection system is based on enzyme-labeled reagents.”