Foodborne Bacterial Infections ◾ 363
is no clear-cut basis for this differentiation, the absence of fever among individuals affected by
both Vib. cholerae and Vib. mimicus is used to separate the two species from Vib. parahaemolyticus
and Vib. vulnificus infection.
Vibrio parahaemolyticus 40,41
Importance
Gastroenteritis caused by Vib. parahaemolyticus is quite common in Japan and accounts for 40%–
70% of the total bacterial foodborne diseases. The high incidence is directly related to the consumption of raw seafoods, such as oysters. In the United States, its involvement in foodborne
infection was first recognized in 1971 from a large outbreak associated with the consumption
of steamed crabs contaminated with the pathogen following heat treatment. Several other largescale outbreaks were confirmed in the 1970s. However, in the 1980s, the number of outbreaks
and number of cases per outbreak reduced greatly. Between 1980 and 1987, there were only 12
outbreaks involving a total of 75 people and no fatalities. Between 2009 and 2010 there were four
outbreaks associated with 33 illnesses. 32 The CDC estimates annually about 35,000 people acquire
Vib. Parahaemolyticus, and 86% of them are foodborne in the United States. 29 Vib. parahaemolyticus serovars O3:K6 is associated with outbreaks worldwide, and other serotypes, O4:K68 and
O1:KUT, are increasingly associated with foodborne diseases.
Characteristics
The cells are gram-negative, nonsporulating, and motile with straight or curved rods. They are
generally catalase and oxidase positive. Vib. parahaemolyticus cells are either swimmer-aided by a
single polar flagellum or swarmer resulting from the presence of lateral flagella. The strains grow
in a medium containing glucose without producing gas but are unable to ferment lactose and
sucrose. They can grow over a temperature range of 5°C–42°C with the optimum at approximately 30°C–37°C. The cells are halophiles and multiply rapidly in the presence of 3%–5% NaCl
but are sensitive to 10% salt. Under optimum growth conditions, cells can multiply in approximately 15 minutes. Growth is restricted at pH 5.0 or below. The cells are extremely sensitive to
drying, heating (pasteurization), and refrigeration and freezing.
Habitat
Vib. parahaemolyticus strains are halophilic bacteria distributed in coastal waters worldwide. They
are found in estuarine environments and show a seasonal variation, being present in the highest
numbers during the summer months. During the winter months, they remain in the estuarine
bottom on chitinous materials of plankton.
Virulence Factors and Toxin Production
Not all strains of Vib. parahaemolyticus are pathogenic. The foodborne pathogenic strains produce
many virulence factors: thermostable direct haemolysin (TDH), TDH-related haemolysin (TRH),
sidero phores (called vibrioferrin), and Type 3 secretion system (T3SS). In addition, capsule (K antigens) and biofilm productions help in pathogenesis. TDH (23-kDa hemolysin) is considered to
be the most important toxin. TDH producers are designated as Kanagawa phenomenon-positive,
is no clear-cut basis for this differentiation, the absence of fever among individuals affected by
both Vib. cholerae and Vib. mimicus is used to separate the two species from Vib. parahaemolyticus
and Vib. vulnificus infection.
Vibrio parahaemolyticus 40,41
Importance
Gastroenteritis caused by Vib. parahaemolyticus is quite common in Japan and accounts for 40%–
70% of the total bacterial foodborne diseases. The high incidence is directly related to the consumption of raw seafoods, such as oysters. In the United States, its involvement in foodborne
infection was first recognized in 1971 from a large outbreak associated with the consumption
of steamed crabs contaminated with the pathogen following heat treatment. Several other largescale outbreaks were confirmed in the 1970s. However, in the 1980s, the number of outbreaks
and number of cases per outbreak reduced greatly. Between 1980 and 1987, there were only 12
outbreaks involving a total of 75 people and no fatalities. Between 2009 and 2010 there were four
outbreaks associated with 33 illnesses. 32 The CDC estimates annually about 35,000 people acquire
Vib. Parahaemolyticus, and 86% of them are foodborne in the United States. 29 Vib. parahaemolyticus serovars O3:K6 is associated with outbreaks worldwide, and other serotypes, O4:K68 and
O1:KUT, are increasingly associated with foodborne diseases.
Characteristics
The cells are gram-negative, nonsporulating, and motile with straight or curved rods. They are
generally catalase and oxidase positive. Vib. parahaemolyticus cells are either swimmer-aided by a
single polar flagellum or swarmer resulting from the presence of lateral flagella. The strains grow
in a medium containing glucose without producing gas but are unable to ferment lactose and
sucrose. They can grow over a temperature range of 5°C–42°C with the optimum at approximately 30°C–37°C. The cells are halophiles and multiply rapidly in the presence of 3%–5% NaCl
but are sensitive to 10% salt. Under optimum growth conditions, cells can multiply in approximately 15 minutes. Growth is restricted at pH 5.0 or below. The cells are extremely sensitive to
drying, heating (pasteurization), and refrigeration and freezing.
Habitat
Vib. parahaemolyticus strains are halophilic bacteria distributed in coastal waters worldwide. They
are found in estuarine environments and show a seasonal variation, being present in the highest
numbers during the summer months. During the winter months, they remain in the estuarine
bottom on chitinous materials of plankton.
Virulence Factors and Toxin Production
Not all strains of Vib. parahaemolyticus are pathogenic. The foodborne pathogenic strains produce
many virulence factors: thermostable direct haemolysin (TDH), TDH-related haemolysin (TRH),
sidero phores (called vibrioferrin), and Type 3 secretion system (T3SS). In addition, capsule (K antigens) and biofilm productions help in pathogenesis. TDH (23-kDa hemolysin) is considered to
be the most important toxin. TDH producers are designated as Kanagawa phenomenon-positive,