Fundamental Food Microbiology, Third Edition - Fuad Fathir

FOODBORNE INFECTIONS 381
2. Characteristics
The cells are Gram-negative, nonsporulating, motile, curved rods. They are generally
catalase and oxidase positive. 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 to 42�C, with the optimum ca. 30 to 37�C. The cells
multiply rapidly in the presence of 3 to 5% NaCl but are sensitive to 10% salt. Under
optimum growth conditions, cells can multiply in ca. 15 min. Growth is restricted
at pH 5.0 or below. The cells are extremely sensitive to drying, heating (pasteurization),
and refrigeration and freezing. 33–35
3. 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. 33–35
4. Toxin and Toxin Production
Not all strains of Vib. parahaemolyticus are pathogenic. The foodborne pathogenic
strains can cause hemolysis because of the presence of a heat-stable hemolysin and
are designated as Kanagawa-positive. At present, the 23-kDa heat-stable hemolysin
(called thermostable direct hemolysin, TDH) is considered to be the toxin. Most
strains isolated from natural sources (estuarine water, plankton, shellfish, and finfish)
are Kanagawa-negative. However, some Kanagawa-negative strains have also been
associated with foodborne outbreaks. All pathogenic strains were found to adhere
to human fetal intestinal cells in cell cultures. The toxin production rate and its level
are directly related to cell growth, cell concentrations, and pH of the environment.
If the toxin forms (in a food), heating does not destroy it. 33–35
5. Disease and Symptoms
The cells are sensitive to low stomach pH. Generally, an individual has to consume
10 5–7 cells of a Kanagawa-positive strain for symptoms to develop. However, an
increase in pH from consumption of bicarbonates and foods can reduce the infective
dose. Symptoms appear 10 to 24 h following ingestion of live cells and last for 2
to 3 d. Symptoms include nausea, vomiting, abdominal cramps, diarrhea, headache,
fever, and chills. The disease is not normally fatal. 33–35
6. Food Association
Vib. parahaemolyticus strains have been isolated in high numbers from various types
of seafoods harvested from the estuarine environments, especially during the summer
months. The outbreaks, as well as sporadic cases of gastroenteritis, were linked to
the consumption of raw, improperly cooked, or postheat-contaminated seafoods,
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