Seafood Safety

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Description

Vibrio parahaemolyticus is part of the normal flora of estuarine and other coastal areas throughout most of the world. The optimal temperature for growth of V. parahaemolyticus is 37C, although it will grow well at 25-44C (Blake et al., 1980).

In most areas, bacterial densities increase during the warmer months, and as a result, most outbreaks of V. parahaemolyticus illness in the U.S. occur during the summer (Watkins and Cabelli, 1985). Seasonal variation of V. parahaemolyticus in the Gulf of Mexico is not as evident. Studies which investigated V. parahaemolyticus levels in Galveston Bay blue crabs (Davis and Sizemore, 1980) and Louisiana oysters (Paille et al., 1987) showed increased concentrations during the summer months. However, seasonal variation was not observed in V. parahaemolyticus levels in Galveston Bay oysters (Thompson and Vanderzant, 1976a).

Pathogenic strains of V. parahaemolyticus cause hemolysis on Wagatsuma agar (the Kanagawa phenomenon). It has been reported that over 95% of the isolates from individuals with gastroenteritis are hemolytic, or Kanagawa positive (Joseph et al., 1983, as cited in Morris and Black, 1985). However, only 0.18% (Thompson and Vanderzant, 1976b) to 1% (Joseph et al., 1983, as cited in Morris and Black, 1985) of the environmental isolates are K+. A number of theories have been suggested to explain the greater proportion of K+ strains from gastroenteritis isolates than from environmental isolates. It is possible that the present isolation methods do not favor the detection of K+ strains, and are therefore underestimating the number of hemolytic strains in the environment (Hackney et al., 1980). It has been suggested that a small number of pathogenic strains exist in the environment among a large number of nonpathogenic strains (Nolan et al., 1984; Thompson and Vanderzant, 1976b). However, a study which investigated the survival patterns of K- and K+ strains of V. parahaemolyticus in the environment found no selective advantage of K- strains in the natural environment (Karunasagar et al., 1987). And finally, the organisms may acquire the hemolysin(s) in the intestinal tract of humans (Thompson and Vanderzant, 1976b). However, studies in which human volunteers ingested K- strains of V. parahaemolyticus did not become ill with gastroenteritis (Senyal and Sen, 1974, as cited in Thompson and Vanderzant, 1976b).

The generation time of V. parahaemolyticus has been reported to be as short as nine minutes under ideal conditions (Katoh, 1965, as cited in Blake et al., 1980). Barker (1974, as cited in Bachman et al., 1983) calculated that at this rapid rate of replication, 10 bacteria would lead to 1 million bacteria within 3 to 4 hours.

Contaminated Species

V. parahaemolyticus illness has been associated with consuming contaminated crabs, oysters, shrimp and lobster (Thompson and Vanderzant, 1976a). One outbreak of V. parahaemolyticus gastroenteritis was traced to depurated oysters (Barrow and Miller, 1969, as cited in Richards, 1988), supporting the laboratory evidence that vibrio bacteria do not depurate well (Eyles and Davey, 1984).

Geographical Area

V. parahaemolyticus has been isolated from the Atlantic (Watkins and Cabelli, 1985; Hackney, et al., 1980), Pacific (Nolan et al., 1984) and Gulf Coasts (Thompson and Vanderzant, 1976a).
Symptoms & Treatment

Gastroenteritis caused by V. parahaemolyticus is generally mild to moderate in severity. The onset of symptoms is usually within 4 to 96 hours of consuming contaminated seafood (Morris and Black, 1985). The most commonly experienced symptoms include: diarrhea, abdominal cramps, nausea, vomiting and headache. Fever and chills are less frequently reported (Bryan, 1987; Morris and Black, 1985; Blake et al., 1980). Gastroenteritis caused by V. parahaemolyticus is usually a self-limited illness, lasting a median of 3 days (Morris and Black, 1985).

Vibrio parahaemolyticus can also cause septicemia, and ear and wound infections (Blake et al., 1980). The one reported case of septicemia involved an individual who had a preexisting immunocompromising disease (cirrhosis).

Statistics

V. parahaemolyticus was first recognized as pathogen in Japan in the early 1950's (Blake et al., 1980). In 1969, there were several unconfirmed outbreaks of gastroenteritis in the U.S. that were thought to be caused by V. parahaemolyticus (USDHEW, 1969, as cited in Thompson and Vanderzant, 1976a). From 1977 to 1981 there were nine outbreaks of seafood-borne V. parahaemolyticus illness reported to the CDC (USFDA, 1984).

Detection & Protection

Traditional indicator species do not accurately detect the presence of V. parahaemolyticus, since it is a naturally occurring bacterium (Hackney et al., 1980; Thompson and Vanderzant, 1976a). Illness can be prevented by thoroughly cooking shellfish and by bandaging open wounds to prevent exposure to seawater.


Vibrio Vulnificus

Description

Vibrio vulnificus, originally thought to be V. parahaemolyticus, is a naturally occurring, lactose fermenting bacterium. It requires salt and is commonly isolated at salinities of 7-16 ppt (Kelly, 1982). Sampling in the Gulf of Mexico showed that the organism is seldom found in water temperature <25C, and that the incidence of recovery increases steadily as water temperatures rise. Highest densities in the Gulf are found after water temperatures exceed 25C for several months. Laboratory studies demonstrate an optimal growth temperature of 37C (Kelly, 1982).

Contaminated Species

Cases of V. vulnificus sepsis have been associated with the consumption of oysters and blue crabs (Blake et al., 1980).

Geographic Area

Vibrio vulnificus is primarily found in the Gulf of Mexico (Kelly, 1982), but has also been isolated from the Atlantic (Oliver et al., 1983, as cited in O'Neill et al., in press) and Pacific Oceans (Kaysner et al., 1987, as cited in O'Neill et al., in press). In the Gulf, cell densities are highest during the warmer months, usually April through October (Blake, 1983; Kelly, 1982). The organism has been recovered from shellfish harvested as far north as Maine (O'Neill, et al., in press).



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