Transcript Foodborne Toxicoinfections

Characteristics of Foodborne
Toxicoinfections
For sporeformers, ingestion of large numbers of live
vegetative cells is usually necessary.
Vegetative cells of sporeformers do not multiply in the
digestive tract, but sporulate and release toxins.
For gram-negative bacteria, after ingestion they
Rapidly multiply in the digestive tract.
Many cells also die, releasing toxins.
Toxins of both groups(sporeformers and Gramnegative bacteria) produce the gastroenteritis
symptoms.
Clostridium perfringens
Gastroenteritis
The outbreaks generally occur with some foods that
were prepared in advance by heating and then kept
warm for several hours before serving.
As the disease produces mild symptoms, many
incidents are probably not reported.
Characteristics
The cells are Gram-positive rods, motile and
sporeformers. They grow under anaerobic conditions
but can tolerate some oxygen. The vegetative cells are
sensitive to pasteurization but the spores are
extremely heat resistant.
They can grow very effectively in many protein
foods.
The temperature of growth of vegetative cells and
germination of spores is between 10-52C.
The optimum growth occurs at 45C.
Habitat
Spores and vegetative cells are found in soil, dust,
intestinal contents of animals, birds, humans and
sewage. Many foods particularly raw foods get
contaminated from these sources.
Toxins
Clostridium perfringens type A strains are
predominantly involved in foodborne
toxicoinfection.
They produce heat-labile enterotoxin.
It is an intracellular protein produced by the cells
during sporulation in the intestine and released.
In addition to the intestine, sporulation ane
enterotoxin production can also occur in some
foods.
Disease and Symptoms
The enterotoxin causes gastroenteritis.
The symptoms appear 8-24 h following ingestion of a
large number of viable cells(about half million cells/g).
Symptoms include diarrhea, abdominal pain, nausea,
vomiting and fever.
The toxin changes the permeability of intestinal cells.
Fatality is rare, but it can occur in very young, elderly
and sick.
Symptoms disappear within 24 h.
This disease is considered a mild one.
Food Association
Raw meat from animals and birds is most
commonly contaminated with the spores and cells
from the digestive tract content, whereas
vegetables and spices commonly get them from
soil and dust.
Contributing factors for outbreaks are the improper
holding temperature of foods, inadequate cooking,
and contaminated equipment.
The foods may not show any loss of acceptance
quality.
Prevention
Proper sanitation in all phases of food preparation and
handling.
Food should be cooked to the highest temperature
recommended to kill the cells and as many spores as
possible.
The food should be cooled quickly and uniformly
To refrigerated temperature.
If a food is stored for a long time, it is important to reheat it
quickly and uniformly and keeping it hot while being served.
Detection Method
Enumeration of the incriminated food and fecal samples for
Clostridium perfringens in a selective agar medium and
incubation of plates under anaerobic conditions.
Bacillus cereus Gastroenteritis
Charachteristics
The cells are Gram-positive motile rods, which form
endospores in the middle of the cells.
Cells are sensitive to pasteurization.
Spores can survive high heat treatment used in many
cooking procedures.
The organism is aerobic, but can also grow under
some degree of anaerobic environment.
The cells can multiply in a temperature range of
4-50C, with the optimum of 35-40C. They can grow in
the presence of high salt concentration.
Habitat
Spores and cells of B. cereus are common in soil and
dust and can be readily isolated from many foods
which include both raw and finished products.
Intestinal tracts of 10% of healthy adult humans have
B.cereus under normal conditions.
Toxins
The strains produce two enterotoxins(emetic and
enteric).
The toxins are produced during growth of cells at the
growth temperature range and retained in the cells.
When the cells are lysed, the toxins are released.
Disease and Symptoms
A large number of cells(2-3 million cells/g) are
needed to produce gastroenteritis.
The two types of enterotoxins produce two types
of symptoms:
The enterotoxin associated with the diarrheal form
is a heat-labile protein, and that associated with
the emetic form is a heat-stable protein.
In diarrheal form, symptoms occur 6-12 h following
consumption of a food containing the viable cells.
Symptoms include abdominal pain, profuse watery
diarrhea. Recovery is usually within 24 h.
In the emetic form, the symptoms occur
in 1-5 h following ingestion of a food
containing the viable cells. As the toxin is
heat stable, once the toxin forms in cells,
heating food containing a large number
of cells before eating can produce the
symptoms.
Symptoms are nausea and vomiting,
abdominal pain and diarrhea may also be
present. Symptoms last for 24 h.
Cholera
Vibrio cholerae is a Gram-negative motile with
monotrichous flagellum, comma-shaped, facultative
anaerobic.
Two serogroups of V. cholerae:
01 and 0139 they cause outbreaks but 01 serogroup
causes the majority of cases.
V. Cholerae 01 has 2 biotypes;
Classical and El Tor
Each biotype has three serotypes; Inaba, Ogawa and
Hikojima.
Non 01 serotype strains are isolated from coastal
waters.
The type currently associated with cholerae
epidemics worldwide is of the El Tor biotype and
either Inaba or Ogawa serotype.
V. cholerae is sensitive to heat and are killed by
the temperature used for cooking.
The optimum temperature of growth is between
30-35C. The growth rate is very rapid even at room
temperature.
Alkaline foods facilitate rapid growth.
Survival of cells is better in cooked foods at 5-10C.
Habitat
Cholera is a human disease.
The disease results from ingestion of
infective doses of V. cholerae( about one
million cells) through foodsand water
contaminated with feces of humans suffering
from the disease.
Marine environments may serve as long-term
reservoirs. Both serotypes, especially non-01,
have been isolated from water in U.S.
Toxins and Toxin Production
The toxin of the 01 serotype is a heat-labile,
85-kDa cytotoxic protein with two functional units.
The active A subunit stimulates adenyl cyclase in the
intestinal epithelial cells to produce cyclic AMP which
causes massive secretion of water along with chloride,
potassium, and bicarbonate in the lining of the
intestine.
The non-01 serotype produces a cytotoxin and a
hemolysin.
Treatments consist of rapid replacement of fluids,
electrolytes and administration of proper antibiotics.
Food Association
Food can serve as a source of V. cholerae if it is
contaminated directly with human feces from the
patient or previously contaminated water.
The handling of food by a person suffering from the
disease can also contaminate food, because of poor
personal hygiene.
Food originating from natural reservoirs of the
causative bacteria can be contaminated and spread
cholera. The natural reservoirs include marine and
brackish water environments.
Among the types of contaminated foods are raw
oysters,
Crab, fish and shrimp and cooked rice.
Prevention
Adopting proper hygienic measures.
Provision of properly treated municipal water.
Decontamination of suspected water by boiling.
Proper disposal of sewage.
Treating of infected persons with antibiotics along
with replacing body fluids.
Vaccination of unexposed people.
Seafoods should not be eaten raw.
Detection Methods
Isolation of V. cholerae from a sample is achieved
by an initial preenrichment in alkaline peptone
water, followed by streaking on a selective agar
medium plate such as thiosulfate citrate bile salt
sucrose agar.
Suspected colonies(yellow) are biochemically and
serologically tested for confirmation.
The toxin is detected by immunoassay.