- The consumption of seafood in the United States has increased rapidly in recent years due to high quality protein and health benefits of seafood. Seafood can be a carrier for bacteria normally distributed in the marine environment and, in some cases, can be contaminated by human pathogens. Therefore, there is a potential health risk if seafood is consumed raw or undercooked. However, information regarding prevalence of foodborne
pathogens in retail seafood products and the ability of pathogens to survive in the products during refrigerated and frozen storage is limited. The objective of this study was to generate such information for a better understanding of distribution of foodborne pathogens in seafood products and provide data which might be used for risk assessment of foodborne infection associated with seafood consumption.
A total of 45 seafood products were collected from local retail stores and analyzed for aerobic plate counts (APC) and psychrotrophic bacterial counts (PBC) as well as presence of foodborne pathogens, including Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio vulnificus according to procedures described in the U.S. Food and Drug and Administration Bacteriological Analytical Manual (BAM). Presumptive isolates for each foodborne pathogen were further characterized by biochemical reactions using commercial identification kits and confirmed with polymerase chain reaction (PCR) assay.
The samples had bacterial populations ranging from 1.90 to 6.11 CFU/g for APC
and from 2.00 to 6.78 CFU/g for PBC. According to the microbiological criteria of
International Commission on Microbiological Specifications for Foods (ICMSF), all 45
samples were considered acceptable quality (APC < 10⁷ CFU/g, E. coli < 3 MPN/g) with
most samples (93.3%) being good quality (APC < 5 × 10⁵ CFU/g, E. coli < 3 MPN/g).
No E. coli O157:H7, Salmonella, S. aureus, V. parahaemolyticus, and V. vulnificus was
detected in any samples. Two previously frozen shrimp products (4.4%) were confirmed
to carry L. monocytogenes.
Studies of growth and survival of L. monocytogenes (3 strains), S. aureus (2
strains), and Salmonella (2 serovars) in raw yellowfin tuna meat stored at 5 - 7 °C for 14
days revealed that L. monocytogenes had the ability to multiply in the tuna meat during
refrigerated storage while populations of S. aureus and Salmonella were reduced by 1 to
2 log CFU/g after 14 days at 5 - 7 °C.
Studies of holding raw yellowfin tuna meat contaminated with L. monocytogenes,
S. aureus, and Salmonella at -18 ± 2 °C for 12 weeks observed that all three pathogens,
except Salmonella Newport, in tuna samples survived the frozen storage with less than 2-
log of reductions in the populations over 12 weeks of storage. No viable cell of
Salmonella Newport was detected in samples after 42 days storage at -18 °C.
Raw seafood can be a carrier of foodborne pathogens, particularly L.
monocytogenes, and many foodborne pathogens can survive in frozen products for
several months. Consumption of raw or undercooked seafood products may lead to
human infection if the products are contaminated with pathogens. Therefore, sanitation
standard operating procedure (SSOP), good manufacturing practice (GMP) and hazards
analysis and critical control points (HACCPs) programs shall all be implemented in the
seafood industry to prevent seafood products from being contaminated with foodborne
pathogens during handling and processing. Moreover, proper storage of raw seafood
products and avoiding cross-contamination during handling at the retail levels also helps
to minimize risk of human infection associated with ready-to-eat products.