378 ◾ Fundamental Food Microbiology
Prevention
The predominant contributing factors associated with Bac. cereus gastroenteritis, in order of relative importance, are improper holding temperature, contaminated equipment, inadequate cooking, and poor personal hygiene. The heat treatment normally used in food preparation, except for
pressure-cooking, may not destroy Bac. cereus spores. The most important control measure is to
keep food at a temperature at which the spores do not germinate and cells do not grow. This can
be achieved by uniform quick chilling of the food to approximately 4°C–5°C or holding the food
above 60°C. Quick chilling can best be accomplished by storing a food in a shallow container, no
more than 2–3 in. (5–6 cm) thick. Because Bac. cereus cells, given sufficient time, can grow and
produce toxins at refrigerated temperatures (≥4°C), a food should not be stored at low temperatures for long periods of time. This means that preparation of a food well in advance should be
avoided. Because cells can get in a food through cross-contamination, proper sanitary measures
should be adopted while handling a food. Finally, as live cells are necessary for the symptoms,
there should be uniform reheating of a suspected food to above 75°C before serving. However,
heating may not destroy heat-stable toxins associated with emetic symptoms.
Detection Method
Bac. cereus can be enumerated by surface plating on an agar medium containing mannitol, egg
yolk, and polymyxin B (as a selective agent), such as Phenol Red Mannitol agar (PRM), MannitolEgg Yolk-Polymyxin agar (MYP), B. cereus base agar (BCA), and Bacillus cereus chromogenic agar
media (BACARA). Colonies surrounded by precipitation resulting from lecithinase of the cells are
indicative of Bac. cereus. Bac. cereus is hemolytic and produces a zone of hemolysis on a blood agar
plate (Figure 27.2). Bac. cereus toxins could be detected by ELISA and cytotoxicity assays rapidly
using mammalian cells. 11 Molecular methods employing PCR targeting toxin genes are also used
for detection of Bac. cereus.
Vibrio cholerae
Importance
Vibrio species belong to the family Vibrionaceae and are usually found in aquatic environments,
including seawater, fish, sea plankton, coral reefs, and chitinous sea animals. They can also be
found on the body surface and in the gastrointestinal tract of marine animals. The genus Vibrio
contains more than 50 species. Vib. cholerae cause a disease called cholera, which is a noncontagious disease but can cause large epidemics with high mortality. In the 19th century, both
epidemic and isolated cholera cases were recorded in the United States. Since 1911, the disease
was thought to be eradicated. Most of the outbreaks in the 20th century were recorded in Asian
countries. However, in 1973, a cholera case was recorded in Texas. Between 1973 and 1987, six
outbreaks involving 916 cases with 12 deaths were recorded, mostly in the coastal states of the
United States. Contaminated seafoods (cooked crab, finfish, and raw oysters) were involved in
these cases. In 1991 and 1992, a large cholera epidemic that started in Peru spread to many South
American countries and affected approximately 640,000 people, with 5600 deaths. It was also
introduced into the United States by travelers from these countries, who either ate contaminated
foods before entering the United States or brought contaminated concealed foods to the United
States. In addition to the O1 strains, Vib. cholerae non-O1 strains have also been involved in
Prevention
The predominant contributing factors associated with Bac. cereus gastroenteritis, in order of relative importance, are improper holding temperature, contaminated equipment, inadequate cooking, and poor personal hygiene. The heat treatment normally used in food preparation, except for
pressure-cooking, may not destroy Bac. cereus spores. The most important control measure is to
keep food at a temperature at which the spores do not germinate and cells do not grow. This can
be achieved by uniform quick chilling of the food to approximately 4°C–5°C or holding the food
above 60°C. Quick chilling can best be accomplished by storing a food in a shallow container, no
more than 2–3 in. (5–6 cm) thick. Because Bac. cereus cells, given sufficient time, can grow and
produce toxins at refrigerated temperatures (≥4°C), a food should not be stored at low temperatures for long periods of time. This means that preparation of a food well in advance should be
avoided. Because cells can get in a food through cross-contamination, proper sanitary measures
should be adopted while handling a food. Finally, as live cells are necessary for the symptoms,
there should be uniform reheating of a suspected food to above 75°C before serving. However,
heating may not destroy heat-stable toxins associated with emetic symptoms.
Detection Method
Bac. cereus can be enumerated by surface plating on an agar medium containing mannitol, egg
yolk, and polymyxin B (as a selective agent), such as Phenol Red Mannitol agar (PRM), MannitolEgg Yolk-Polymyxin agar (MYP), B. cereus base agar (BCA), and Bacillus cereus chromogenic agar
media (BACARA). Colonies surrounded by precipitation resulting from lecithinase of the cells are
indicative of Bac. cereus. Bac. cereus is hemolytic and produces a zone of hemolysis on a blood agar
plate (Figure 27.2). Bac. cereus toxins could be detected by ELISA and cytotoxicity assays rapidly
using mammalian cells. 11 Molecular methods employing PCR targeting toxin genes are also used
for detection of Bac. cereus.
Vibrio cholerae
Importance
Vibrio species belong to the family Vibrionaceae and are usually found in aquatic environments,
including seawater, fish, sea plankton, coral reefs, and chitinous sea animals. They can also be
found on the body surface and in the gastrointestinal tract of marine animals. The genus Vibrio
contains more than 50 species. Vib. cholerae cause a disease called cholera, which is a noncontagious disease but can cause large epidemics with high mortality. In the 19th century, both
epidemic and isolated cholera cases were recorded in the United States. Since 1911, the disease
was thought to be eradicated. Most of the outbreaks in the 20th century were recorded in Asian
countries. However, in 1973, a cholera case was recorded in Texas. Between 1973 and 1987, six
outbreaks involving 916 cases with 12 deaths were recorded, mostly in the coastal states of the
United States. Contaminated seafoods (cooked crab, finfish, and raw oysters) were involved in
these cases. In 1991 and 1992, a large cholera epidemic that started in Peru spread to many South
American countries and affected approximately 640,000 people, with 5600 deaths. It was also
introduced into the United States by travelers from these countries, who either ate contaminated
foods before entering the United States or brought contaminated concealed foods to the United
States. In addition to the O1 strains, Vib. cholerae non-O1 strains have also been involved in