Dar seafood ppp standard

Table 1.2: Potential food safety hazards along the molluscan shellfish supply chain

Supply chain sector	Source of hazards	Examples of hazards
Pre-harvest	Bacterial, viral and chemical contamination by sewage and runoff	Enteric pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes, hepatitis A virus, noroviruses) Agricultural chemical residues
	Exposure to environmental contaminants	Endogenous bacteria that are human pathogens (A. hydrophila, V. parahaemolyticus, V. vulnificus, V. cholerae O1, non-O1/non-O139 V. cholerae Chemical (algal biotoxins, mercury, cadmium, zinc)
Depuration and shucking	Contamination by shuckers	Microbiological pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes, hepatitis A virus, noroviruses)
	Opportunity for outgrowth	Bacterial pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes, A. hydrophila, V. parahaemolyticus, V. vulnificus, V. cholerae O1, non-O1/non-O139 V. cholerae)
	Reduction in level of hazards due to depuration	Reduced levels of some bacterial pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes)
Transport, marketing, retailing and food service	Contamination by food handlers	Microbiological pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes, hepatitis A virus, noroviruses)
	Opportunity for outgrowth	Bacterial pathogens (E. coli, S. aureus, Salmonella spp., Campylobacter spp., Shigella spp., Yersinia spp., L. monocytogenes, A. hydrophila, V. parahaemolyticus, V. vulnificus, V. cholerae O1, non-O1/non-O139 V. cholerae)

Effects of processing on levels of hazards in molluscan shellfish

Oysters

Pre-harvest: Oysters are filter feeders, extracting marine algae, bacteria and nutrients from the surrounding waters. Because of this, they are prone to contamination from the growing environment, and concentrate certain chemical hazards as well as support viability and/or growth of microbiological contaminants. In Australia, oysters are mainly grown on aquaculture leases in estuarine environments, often close to populated or tourist recreational areas.
Some pathogenic bacteria are endogenous to aquatic environments and can survive or grow in oysters, presenting a risk to health if ingested. These include V. vulnificus, pathogenic strains of V. parahaemolyticus and V. cholerae, and Aeromonas hydrophila. Typically, levels of these pathogens in the environment will be low, being subject to environmental conditions such as salinity and water temperature.
In Australia, A. hydrophila, V. vulnificus and pathogenic strains of V. parahaemolyticus are present in estuarine environments where oysters are grown commercially. However, only non-toxigenic strains of V. cholerae O1 have been isolated from estuarine environments and oysters [1].

Microbiological hazards may also be introduced into oyster growing waters through pollution from sewage and animal waste. These pathogens typically survive for only short periods of time in the marine environment, but maintain viability for much longer when ingested by oysters. Examples include pathogenic strains of E. coli and Salmonella, Campylobacter, Yersinia and Shigella species. These organisms can multiply quickly, particularly at higher temperatures, potentially rendering oysters unsafe for consumption.

Pathogenic viruses, particularly hepatitis A and the small round structured viruses (noroviruses of the caliciviridae family) may be introduced to oyster growing waters through sewage pollution and can survive for long periods in oysters. While viruses will not replicate in shellstock, they have low infectious doses, and thus present a risk to human health.
Oysters can also extract chemical contaminants from their growing waters, and bioaccumulate them to hazardous concentrations in their flesh. Industrial, agricultural and sewage pollution may introduce various hazardous chemical into waterways where oysters are grown, while natural sources of heavy metals may also be of concern.
Certain species of toxin-producing marine dinoflagellate and diatomic algae present a food safety risk from oyster consumption. The algae and toxins can potentially accumulate to high concentrations in oysters, particularly during periods of algal bloom (for example, red tides) when levels of the algae suddenly increase in response to environmental triggers. The combination of factors triggering bloom events is not fully understood, and toxin concentrations do not necessarily correlate with levels of the algae in the marine environment, making it difficult to predict the degree of food safety risk from these hazards.
Post-harvest: Processing of oysters before retail sale is usually minimal. When necessary, algae adhering to the shell are removed by tumbling, a process that can result in some damage to the oyster shells and potentially allow contamination of the meat. Oysters may be purified to some extent by relaying or depuration. These processes are reasonably efficient at reducing the load of enteric bacteria in oysters, but are significantly less effective at reducing the levels of viruses, endogenous marine pathogenic bacteria, chemicals and algal biotoxins.
The main processing of oysters involves shucking and packing in boxes for sale on the half shell or bottling in fresh water, depending on the grade. The shucking process does not kill pathogenic micro-organisms or remove chemical contaminants, but introduces the potential for further contamination by enteric pathogens. In addition, the potential exists during shucking and transportation for temperature abuse, allowing multiplication of bacterial pathogens to levels that might pose a public health risk. Further handling in the distribution chain also carries with it the potential for contamination and temperature abuse.