CONTROL (crustacea)

Summary

Signiﬁcant hazards a r Vibrio spp. (if consumed raw). r Enteric pathogenes (if consumed raw).

Control measures

Initial level (H 0 )

r Avoid catching in contaminated waters.

Reduction (Σ R)

r Cooking destroy vegetative pathogens.

Increase (Σ I)

r Time × −temperature.

Testing

r Sensory evaluation.

Spoilage

r Growth of spoilage bacteria. r Time × −temperature;. r Sensory evaluation.

a In particular circumstances, other hazards may need to be considered.

201 Hazards to be considered. The health hazards of raw crustaceans are in some ways similar to other

FISH AND FISH PRODUCTS

raw ﬁsh products. However, aquatic toxins are generally not accumulated, no formation of biogenic amines occurs and parasites have not been reported. Both viral and bacterial pathogens are potential hazards if the product is eaten, raw or if re-contamination occurs after a cooking step. If the product is hand peeled, pathogens can be introduced. Most hand peeling is probably done on cooked shrimp, and the speciﬁc hazards related to this are discussed in a later section. If the product is peeled in the raw state, subsequent cooking will eliminate pathogenic organisms.

Control measures. Most of the controls for maintaining the microbiological integrity of raw shrimp are the same as those outlined for finfish (see above), including harvesting from quality fishing grounds, rapid chilling after capture, maintenance of sanitation, and avoidance of cross-contamination.

Initial level of hazard (H 0 ). Because shrimp are harvested by trawling, the animals should be washed immediately with fresh sea-water to remove mud and sediment, reducing initial levels of contamination (H 0 ).

Reduction of hazard (Σ R). Excessive handling of shrimp by humans can be a source of salmonellae, Staph. aureus , and other pathogens. Fortunately, such bacteria are usually destroyed by the normal cooking procedures to which crab, lobsters, and most shrimp are subjected, relying on a reduction step (ΣR) for safety. However, cooking may not destroy all bacteria if the initial levels are high. There are

reports of bacterial counts as high as 3.7 10 5 cfu/g in crab boiled for 30 min and 4.5 × 10 4 cfu/g oin tropical prawns after boiling for 3 min, however, re-contamination (Σ I ) of cooked products is the major issue for control.

Increase of hazard (Σ I). If the shrimp are to be headed at capture, it should be done at once. Immediately after capture, the shrimp should be iced on board ship and maintained on ice or under refrigeration to avoid increase of pathogenic bacteria (ΣI). The temperature should be reduced to <5 ◦ C within 2 h after catch. Picking, when done by adequately maintained peeling machine, is generally a sanitary processing step preventing re-contamination, i.e. increase (ΣI). Sanitary design and proper cleaning of machines is needed to avoid accumulation of shrimp parts on the equipment. An equivalent level of control is difﬁcult to achieve when shrimp are hand peeled, particularly if carried out under less than ideal sanitary conditions. A primary control for crabs and lobsters is maintaining them alive and healthy until cooking, thus preventing increase (ΣI) of pathogenic or spoilage bacteria. This means careful handling; storage longer than a few hours requires immersion in cool aerated sea-water. During storage, temperatures should be checked and there should be monitoring for dead animals, which should

be removed promptly.

Testing. Microbiological indicators do not appear to be effective for predicting the presence of salmonellae in shrimp (D’Aoust et al., 1980). Vibrio spp. are indigenous, aquatic, bacteria and must be as- sumed to be present. Hence, processing and handling should ensure that there is no cross-contamination to cooked products. As for fresh ﬁnﬁsh, testing of raw crustaceans for Vibrio spp. is not useful for assuring safety.

Spoilage. Raw, iced crustaceans spoil in the same manner as fresh ﬁnﬁsh, and time-temperature control is the most important control measure. Preferably, the crustaceans should be kept in melting ice at ∼0 ◦ C.

MICROORGANISMS IN FOODS 6

C Mollusca The animals included in this section are all bivalve molluscs, which feed by selectively ﬁltering out

small planktonic organisms, including bacteria, from sea-water. They include principally clams, mussels, cockles, oysters, and scallops.

Harvesting and processing procedures. Clams grow buried a few centimeters to a meter or more in marine and fresh water sediments. They are harvested by mechanical dredges, by scuba divers with air or water jets, and by digging by hand at low tide. Most are wild populations that depend on natural processes for seeding and renewal, but in recent years there has been increased use of artiﬁcial enhancement of natural populations and closed cycle aquaculture of clams. Mussels grow naturally attached to rocks, cliffs, and other surfaces that are tidally submerged. They are cultivated throughout the world on submerged strings suspended from rafts or other ﬂoating structures from which they are readily harvested. They are harvested by hand. Oysters occur naturally in estuarine areas in and below tidal areas, growing on the surface of sediments. They have been cultivated by selective relaying of captured spat for centuries, and in recent years controlled production of seed in hatcheries has led to more controlled aquaculture. However, growing oysters depend on natural food sources in sea-water. They are harvested by hand picking, tonging, raking, or mechanical dredges. Often, oysters are kept in clean (disinfected) water for some days to allow clearance of some pathogenic agents (see below).

All these animals are naturally sessile in the adult form but have the capacity to close their shells tightly enabling them to survive for long periods out of water. They are normally held in a live state until processed or through distribution and retailing in the case of unprocessed animals. They are frequently eaten live after removal from the shell (shucking). Transport on ice is recommended. An example of a typical process ﬂow diagram for molluscs is provided in Figure 3.6.

Scallops are somewhat more mobile animals but generally congregate in limited areas, moving short distances in fairly shallow water by forcing a jet of water through partly closed shells. They are caught by dredges and may be shucked on-board the vessel or brought ashore in the shell. Typically, only the adductor muscle is eaten in North America and much of Europe. This is the major product in international trade, but whole scallops are commonly eaten by a number of cultures and by gourmets.

Oysters, mussels, and clams may be marketed as whole live animals in the shell or as shucked meat. Whole clams may be frozen in the shell. Shucked meats are sold from bulk stocks with individual wrapping for the customer or they may be packaged in plastic containers or glass jars at the processing plant and shipped under refrigeration. Shucking is mainly a hand operation. Oyster processing also involves a mechanical “blowing” operation, which involves tumbling the shucked meats in vigorously aerated fresh water. This removes shell fragments and “plumps” the oysters.

Saprophytes and spoilage. Molluscs carry a resident bacterial population that in the case of oysters ﬂuctuates between 10 4 and 10 6 cfu/g of tissue, the higher counts occurring when water temperatures are high. The microﬂora is dominated by Gram-negative bacteria of the genera Vibrio–Pseudomonas– Acinetobacter—Moraxella , Flavobacterium, and Cytophaga (Colwell and Liston, 1960; Lovelace et al., 1968; Vanderzant et al., 1973). This seems to be the resident population for molluscs. Smaller numbers of Gram-positive bacteria may also be present.

When molluscs feed on polluted water, they concentrate contaminating bacteria, including enteric pathogens and viruses, if present. As oysters and other molluscs harvested for human consumption are normally acquired from estuarine areas that receive some waste from point (sewage) and non-point (run-off) land sources (Stelma and McCabe, 1992; Ekanem and Adegoke, 1995), it is not

FISH AND FISH PRODUCTS

Receive

Dry storage

Wet storage

Heat shock

(steam)

(hot dip)

Hand shuck

Inspect/separation of foot

Wash

Bubble/soak

Grind/chop

Package

Refrigerated storage

Freeze

Repack

Frozen storage

Ship

Figure 3.6 Example of ﬂow diagram for shucked mollusca (NMFS, 1990b).

uncommon for small numbers of mesophilic coliforms to be found. However, they are not part of the normal resident bacterial populations. A possible exception is the presence of large numbers of marine mammals, particularly pinnipeds (seals) and sea-lions, which can contribute to the presence of fecal contamination (Smith et al., 1986).

During spoilage of shucked molluscs, bacterial populations normally increase to 10 7 cfu/g or more. Gram-negative proteolytic bacteria, usually Pseudomonas and Vibrio spp., are prominent in the spoilage flora. In addition, saccharolytic bacteria are active, fermenting the glycogen in the tis- sues to various organic acids. Lactobacillus spp. were reported as a major component of the spoilage microflora and identified as the fermenting organism (Shiflett et al., 1966). However, lactobacilli may not occur consistently in marine products, and when lactobacilli were added to vacuum packed

MICROORGANISMS IN FOODS 6

scallops, they did not inhibit the growth of Vibrio spp. (Bremner and Statham, 1983). However, lactic acid (1.25%) rinses have been used experimentally to retard spoilage (Kator and Fisher, 1995).

Biochemically, spoilage includes both proteolytic and saccharolytic activity. Ammonia and other amines accumulate, but so do acids. The pH of molluscs typically falls during spoilage (in contrast to ﬁnﬁsh and crustacea in which pH increases). Fresh oysters have pH values from about 6.2 to 6.5, but this decreases to 5.8 or below during spoilage.

Pathogens. Raw molluscan shellﬁsh are probably the most common vehicle of seafood-related food- borne disease (Table 3.2). This is easily explained by the fact that the animals are ﬁlter feeders and accumulate pathogenic agents and that they are eaten with no heat treatment.

Molluscan shellfish consistently carry mesophilic Vibrio species. The most commonly found is Vibrio alginolyticus (Baross and Liston, 1970; Matté et al., 1994; Suñén et al., 1995), but V. cholerae non-O1,

V. parahaemolyticus, and V. vulnificus are frequent, particularly when water temperatures are high. Indeed, in warm water regions these microorganisms may be present at a level of hundreds of thousands or even millions per gram of animal meat (Kaspar and Tamplin, 1993), though typically the levels are substantially lower (Matté et al., 1994). In warm water regions where V. cholerae O1 is endemic, the microorganism is found sporadically in molluscs. However, in epidemic situations they can be present in comparably high numbers. Information pertaining to the incidence of V. cholerae O139 (a new epidemic serovar) in molluscan shellfish is not yet available.

Vibrio parahaemolyticus may increase in the live animal if held at high temperature (26 ◦ ), thus numbers in live oysters increased with 1.7 log 10 units in 10 h and with 2.9 log 10 units in 24 h at this temperature (Gooch et al., 2002). In contrast, the number of V. parahaemolyticus decreased (0.8 log 10 unit in 14 days) if kept at refrigeration temperature.

Outbreaks of disease have been reported among individuals eating raw or lightly processed shellﬁsh involving each of these vibrios (Blake, 1983; Klontz et al., 1993; Popovic et al., 1993). In addition,

V. mimicus , V. hollisae, and V. furnissii have been reported associated with occasional shellﬁsh associated outbreaks. The severity of most vibrio infections is mild and patients normally recover quickly and spontaneously after a few days of diarrhea. However, V. cholera O1 can be life threatening if not properly treated, and severe septicemic conditions have been recorded from V. cholerae non-O1,

V. parahaemolyticus , and Vibrio hollisae, though uncommon. A particularly dangerous microorganism for individuals with underlying liver disorders and certain other diseases (e.g. cirrhosis, haemochromato- sis, and diabetes) is V. vulniﬁcus. In such patients, the species can cause a fulminating primary septicemia that can result in death in 24–48 h. Fortunately, the microorganism does not usually cause disease, or produces a mild and self-resolving condition, in healthy individuals. The microorganism is particularly associated with oysters, with nearly all cases resulting from consumption of raw oysters. There are indications that encapsulation of V. vulniﬁcus may increase its survival in oysters (Harris-Young et al., 1995).

Molluscan shellfish are notoriously liable to become contaminated with bacteria derived from human sewage because of their sessile estuarine habitat. In years past, typhoid fever was a common consequence of raw oyster consumption in Europe and North America. This disease and other infections from sewage- derived bacteria including non-specific salmonellosis, shigellosis, etc. have become less common in industrialized countries. This is a consequence of both improved methods of sewage treatment and effective surveillance of shellfish growing areas for human fecal contamination. Nevertheless, even in countries with good regulatory programes some cases still occur, often from contaminated shellfish illegally harvested from closed areas. In Japan, in 2001–2002, raw oysters were the cause of a shigellosis outbreak (Miyahara and Konuma, 2002; Konuma, 2002). It is often not possible to demonstrate a direct relationship between the presence of indicator organisms in the growing water and the presence of

205 speciﬁc pathogens in the shellﬁsh (Hood et al., 1983; Martinez-Manzanares et al., 1992). Campylobacter

FISH AND FISH PRODUCTS

jejuni has been implicated as a cause of shellfish-associated gastroenteritis outbreaks (Griffin et al., 1980; Abeyta et al., 1993). The organism is believed to originate from sea gull feces (Teunis et al., 1997). Some studies failed to detect Campylobacter spp. in molluscs (Ripabelli et al., 1999), whilst others have found as many as 42% of samples positive (Wilson and Moore, 1996). In general, there is a paucity of data and further research in needed to determine the magnitude of the problem. Staph. aureus has been isolated from a substantial percentage of shellfish meat samples (Ayulo et al., 1994), presumably due to handling during shucking; however, due to the large numbers of other bacteria, it is not likely that Staph. aureus will cause disease.

The most common microbiological problem for consumers of molluscs is now viral infections (Liston, 1990; Lees, 2000). Viruses are more resistant to water treatment procedures and therefore more likely to survive in effluent water. Moreover, viruses may survive in marine environments for months, and perhaps years, when water temperatures are low (Boardman and Evans, 1986; Gerba, 1988). This has resulted, at least in the United States, in a pattern of viral disease mainly from clams harvested in cooler northern waters and vibrio gastroenteritis from oysters grown in warmer southern waters. However, shellfish-derived viral and vibrio diseases can occur in both temperature zones. Hepatitis virus (A, non-A/non-B, and unidentified) are transferred by bivalves (IOM, 1991) but Norwalk and Norwalk-like, and other small round viruses are the major cause of gastroenteritis transmitted by foods, including seafoods (ACMSF, 1994; Lees, 2000).

The majority of marine toxins important from a food standpoint are produced by microalgae in the phytoplankton, which is the source of food organisms for molluscs. Toxic algae are not consistently present, at least at levels that could cause dangerous toxicity. Instead, they occur as blooms in response to changes in physical and chemical conditions, which are not entirely understood (Hallegraeff, 1993). The four toxin groups significant to consumers of molluscs are those causing PSP, NSP, DSP, and ASP. The principal toxigenic microorganisms involved are the dinoflagellates Alexandrium (Gonyaulax), Gymnodium and Dinophysis and the pennate diatom Pseudonitzschia. PSP-causing Alexandrium appear to be globally distributed and show a seasonal occurrence along the coasts of North America where blooms occur (unpredictably) from May to September. However, occasional episodes have been reported in winter allegedly due to resuspension of cyst forms in sediment by storms. The pattern appears much more sporadic in other parts of the world. NSP seems only to have been reported in the Gulf of Mexico and Southeast Atlantic coastlines of the United States, but Gymnodinium is quite widespread, as are characteristic red tides, so the hazard may be more extensive than appears. DSP on the other hand seems to be widespread along Japanese and European coastlines but has not been reported in North America. However, the implicated Dinophysis species do occur in both Atlantic and Pacific waters. Domoic acid poisonings (ASP) have been reported from northeastern Canada and the coastline of California, Oregon, and Washington, but the Pseudonitzschia diatoms are probably global in incidence. This disease seems to be associated with cold (5 ◦

C) water temperatures, but information on this is limited. Toxigenic species have been spread from one geographical area to another in the ballast of ocean going ships (Hallegraeff, 1993).

Interrelations. The presence of a large natural population of bacteria does not seem to affect the uptake and short-term survival of potentially pathogenic bacteria and viruses. However, there is not much information available on the growth rates of such organisms during the spoilage of oysters, when the pH drops below 6.0. Palumbo et al. (1985) noted a decline in the numbers of Aero. hydrophila during the refrigerated storage of shucked oysters that corresponded to the pH decline. However, it would be unwise to rely on this pH decline to destroy pathogens because some pathogens can survive for long periods in oysters stored in the shell.

MICROORGANISMS IN FOODS 6

CONTROL (crustacea)